measurement diaphragmatic flow · measurement of diaphragmatic blood flow and oxygen consumption in...

Measurement of Diaphragmatic Blood Flow

and Oxygen Consumption in the Dog

by the Kety-Schmidt Technique

DUDLEYF. RocHmE

From the Cardio-Respiratory Laboratory, Department of Medicine, ColumbiaUniversity, College of Physicians & Surgeons, NewYork 10032

A B s T R A C T To assess energy expenditure of thediaphragm directly, a method was devised for percu-taneous catheterization of the left inferior phrenic veinin dogs. Necropsy studies, including retrograde injectionof india ink and measurement of radioactivity in dia-phragmatic muscle strips, suggested that the territorydrained by the inferior phrenic vein was uniformly per-fused, and that there were no major anastomoses be-tween this bed and adjacent ones.

Diaphragmatic blood flow (Q di) was calculatedfrom the integrated diaphragmatic arteriovenous dif-ference of 8'Kr by the Kety-Schmidt technique. Diaphrag-matic oxygen consumption (V02 di) was determined asthe product of Q di and the diaphragmatic arteriovenousoxygen content difference [ (A-V)02 di]. When lightlyanesthetized dogs breathed quietly, Q di was 22+SD 6ml/min/100 g, (A-V)02 di was 6.1+SD 2.5 ml/100 ml,and V02 di averaged 1.2+SD 0.3 ml/min/100 g. Thisrepresented 1.0±SD 0.2% of total body oxygen con-sumption. VO2 di remained relatively constant duringquiet breathing, whereas Q di varied directly withcardiac output and reciprocally with (A-V)02 di. Theoxygen consumption of the noncontracting diaphragmwas 60+SD 20%- of the level measured during quietbreathing.

The energy expended by the diaphragm to supportsimple hyperventilation was small. A 100% increasein minute ventilation, induced by inhalation of 5% C02in 21% or 14% 02, increased Q di 13%, (A-V)02 di19%, and V02 di 40%. The diaphragm consumed 0.13±

This work was presented in part at the 62nd AnnualMeeting of the American Society for Clinical Investiga-tion, Inc., Atlantic City, N. J., May 1970, and publishedin abstract form (J. Clin. Invest. 1970. 49: 80a.).

Received for publication 4 June 1973 and in revised form4 January 1974.

SD 0.09 ml 02 for each additional liter of ventilation. Infour dogs, pneumonia appeared to increase V02 both byincreasing minute ventilation and by increasing theenergy cost per liter of ventilation.

INTRODUCTIONDiseases characterized by an increased work of breath-ing impose an excessive burden on the respiratorymuscles. Evaluation of the ability of the respiratory mus-culature to sustain acute and chronic increases in workload would be enhanced greatly by knowledge of theblood flow to and oxygen consumption of individual in-spiratory muscles.

Blood flow to the diaphragm and intercostal muscleshas been assessed to only a limited degree. While thedirection of change consequent to certain physiologicinterventions has been established, accurate quantifica-tion of the level of perfusion has not been achieved(1-4). The oxygen consumption of all the respiratorymuscles has been repeatedly evaluated by the indirectmethod of Liljestrand (5-13), but with the exceptionof preliminary results from this laboratory (14), nodata concerning direct measurement of the oxygenconsumption of an individual respiratory muscle havebeen reported.

During an earlier study of diaphragmatic blood flowwe reexamined the arrangement of the veins drainingthe canine diaphragm, and found that tributaries onthe abdominal surface of each hemidiaphragm. join toform common trunks, which enter the inferior vena cavacephalad to the hepatic veins. The trunk on the left is3-4 cm long and about 0.5 cm in diameter at the cavalorifice, which led us to believe it could be catheterizedby conventional percutaneous techniques.

The purposes of this report are, first, to outline thetechniques used to catheterize the left inferior phrenic

The Journal of Clinical Investigation Volume 53 May 1974*1216-12251216

vein and describe the methods used to measure diaphrag-matic blood flow, arteriovenous oxygen difference, andoxygen consumption. Secondly, the determinants ofdiaphragmatic blood flow and oxygen consumption willbe assessed at three levels of diaphragmatic energy ex-penditure: when it is not contracting, when it is sup-porting quiet breathing, and during hyperventilation.Finally, the report will evaluate the diaphragmatic oxy-gen cost of breathing, both in relation to total body oxy-gen consumption and in terms of the energy required toincrease the minute ventilation.

METHODS

Animal preparationAll studies were performed in adult mongrel dogs weigh-

ing 17-37 kg. The animals were initially anesthetized with25 mg/kg of pentobarbital. Upon completion of surgicalprocedures, the level of anesthesia was adjusted with anintravenous drip of 5% thiamylal sodium so that the innercorneal reflex was retained.

The trachea was intubated with a cuffed tube passedthrough the larynx. A double-lumen catheter was advancedvia the right femoral vein so that the distal lumen lay inthe right atrium and the proximal lumen was in the in-ferior vena cava. The proximal lumen was used for main-tenance anesthesia, while the distal lumen was reserved forkrypton infusion or dye injection. A femoral artery wascannulated.

Measurement of diaphragmatic blood flowCatheterization technique. To catheterize the left in-

ferior phrenic vein, a 7 french Hannafee Nash catheter, 80cm long, was fitted with a guide wire that had an adjust-able curve at the tip (Rotoflector, United States Catheter& Instrument Corp., Glen Falls, N. Y.). The catheter hadbeen previously modified by cutting two additional sideholes within 1 cm of the tip in order to prevent the catheterfrom occluding the diaphragmatic venous outflow. Thisassembly was introduced without a curve into the leftfemoral vein and advanced under fluoroscopic control intothe thoracic portion of the inferior vena cava. The tip wasthen curved to a right angle, and the catheter was rotatedso that the tip pointed directly to the left side of the animal.The catheter assembly was then withdrawn to a site justbelow the shadow of the dome of the diaphragm and thecatheter was advanced over the curved guide wire. Whenthe left inferior phrenic vein was entered successfully, thecatheter could be advanced horizontally across the mid-line below the heart shadow until the tip nearly intersectedthe left hemidiaphragm silhouette. To facilitate visualiza-tion of the catheter, 50% aqueous Hypaque solution (Win-throp Laboratories, Div. of Sterling Drug, Inc., New York)was injected. The appearance of the catheter in the phrenicvein and other details of the preparation are depicted inFig. 1. When the catheter entered a hepatic vein instead ofthe left inferior phrenic vein, the catheter always appearedwell below the dome of the diaphragm, and usually pointedin a somewhat caudad direction. Correct catheter positionwas confirmed at necropsy in all animals.

The left inferior phrenic vein was cannulated successfullyin 80% of the animals, but most attempts to catheterizethe right inferior phrenic vein failed. Although the latter

.Endotrachial tube

Infusion 9

DiaphragmaticVem 14 j Femoral artery

FIGURE 1 Diagram of experimental preparation.. The in-fusion is shown entering the right atrium. After the firstset of studies, the infusion catheter was passed retrogradefrom a femoral artery to the left ventricle. See text.

vein could be entered, the trunk was so short that thecatheter usually snapped out spontaneously.

The anatomy of the inferior phrenic venous bed wasfurther explored by retrograde injection of india ink atnecropsy. The muscle sheet between the central tendon andthe chest wall was intensely and uniformly stained. Therewas almost no staining beyond the attachment of the dia-phragm to the chest wall. These findings suggest that theinferior phrenic venous bed in the dog drains primarilydiaphragmatic muscle tissue, without significant anastomosesto venous beds draining other organs.

Administration and measurement of radioactivity. Bloodflow per 100 g of diaphragm was measured by the Kety-Schmidt method (15, 16), as modified by Hansen et al.(17). For each determination, krypton-85 dissolved in salinewas infused intravenously at a rate of 250 ,Ci/min for 20min. In all but the first 15 studies, counting rates wereincreased and the radiation dose was decreased by infusingvia a retrograde arterial catheter into the left ventricle.During and shortly after the infusion, all expired air wascollected in a large spirometer and transferred to balloonsto avoid radioactive contamination of the room air.

Arterial blood krypton concentration rises rapidly afterthe start of the infusion, and achieves stable values withinminutes, whereas the inferior phrenic venous blood tracerlevel rises more slowly toward the equilibrium concentra-tion. Upon abrupt cessation of the infusion, the arterialblood krypton concentration falls rapidly to near zero,while the inferior phrenic venous concentration falls at aslower rate. This is the washout phase (Fig. 2).

To establish the krypton concentration-time curves withaccuracy, it is necessary to sample blood from the femoralartery and inferior phrenic vein at 1-2-min intervals for 15min. The volume of the phrenic vein catheter is about 1ml; it is flushed by withdrawing and discarding 3 ml ofblood before collecting the 4 ml of blood needed for eachanalysis. Blood is sampled at 5-6 ml/min. This rate issimilar to that used by Kety and Schmidt (16). The bloodkrypton concentration was *determined by the method ofHardewig, Rochester, and Briscoe (18).

To determine whether or not blood sampled from theleft inferior phrenic vein was contaminated by retrogradeflow of blood from the inferior vena cava, a separate pro-tocol was carried out for eight runs in three dogs. Salinecontaining 'Xe was infused at a constant rate into theinferior vena cava just cephalad to the femoral veins. Blood

Diaphragmatic Blood Flow and Oxygen Consumption 1217

WASH-OUT

A Venous* Arterial

cpm

Ak200

00 10 20Time, min

FIGURE 2 Arterial blood krypton concentrations, denotedby closed circles (*), and diaphragmatic venous bloodkrypton concentrations, denoted by open triangles (A),during the washout phase, after the infusion had stopped.

was collected simultaneously from the left inferior phrenicvein, the thoracic portion of the inferior vena cava, and afemoral artery. Four sets of samples were collected atapproximately 15, 35, 55, and 75 s after the infusion began.Each sample consisted of exactly 2 ml of blood collected ina disposable 10-ml plastic syringe. The sampling rate wasvaried from 5 to 10 ml/min. The blood xenon concentrationwas measured by counting each syringe in a well counter(Picker Nuclear Intertech, North Haven, Conn.).

Uniformity of blood flow to the left hemidiaphragm wasassessed by measuring radioactivity in excised strips of dia-phragm in three animals. Saline containing dissolved 'Xewas infused at a constant rate into the left ventricle ofthree dogs. After 20 min the infusion was stopped andblood samples were collected at half-min intervals from thefemoral artery and left inferior phrenic vein. After 3 min,at which time the xenon level in inferior phrenic venousblood had fallen to about half the level present just beforethe infusion stopped, the dogs were killed by an overdoseof pentobarbital. The abdomen was opened, the left hemi-diaphragm was excised, and strips weighing about 1.5 gwere cut from representative areas. These pieces were putin screw-top counting vials, which were promptly sealedand counted in a well counter. After counting the wetweight of each piece was measured. To correct for therate at which xenon diffused from the excised strips, somepieces were recounted after successive 10-min intervalexposures to air. All results were expressed as countsper milligram wet weight of tissue.

Calculations. To apply the Kety-Schmidt analysis, it isnecessary to determine both the equilibrium tracer concen-tration at the end of the infusion and the integrated arterio-venous difference in indicator concentration, which is graph-ically represented by the area between the arterial andphrenic venous concentration-time curves (Fig. 2). Themeasured arterial and diaphragmatic venous blood kryptonconcentrations were plotted against time and fitted by eyewith the best curves. Arterial krypton concentrations dur-ing the washin phase were frequently erratic, and since inpreliminary studies there was no significant difference be-tween blood flow and oxygen consumption values measuredfrom the washin as compared to the washout phase, onlydata obtained during the latter period were analyzed.

The diaphragmatic venous blood krypton level frequentlyfailed to reach the arterial level within 20-40 min of in-fusion. When this happened, the venous level was taken asthe equilibrium value, because after cessation of a pro-longed infusion of either xenon or hydrogen, muscle tissueand muscle venous blood tracer levels decay at virtually thesame rate (19, 20).

To obtain the integrated arteriovenous difference, thesmoothed arterial and diaphragmatic venous concentration-time curves were read every half-min, and the differencebetween the curves was computed. The area between thecurves, expressed as the product of the concentration dif-ference and time in minutes, was computed as the sum ofthe differences for each half minute divided by two.

The venous tracer level at the end of the sampling periodwas usually higher than the arterial tracer level, with theresult that there was a persistent arteriovenous tracer con-centration difference. To complete the area between thecurves, it was necessary to adopt an extrapolation proce-dure. The difference between recorded arterial and dia-phragmatic venous tracer curves was plotted as a functionof time on semilogarithmic paper. The tail end of the re-sultant arteriovenous difference curve was fitted with astraight line. The area between the unrecorded parts of thearterial and venous concentration-time curve was then com-puted as the product of the last measured arteriovenousconcentration difference and the time constant of the tailof the arteriovenous concentration difference curve.

The ratio of equilibrium tracer concentration to theintegrated arteriovenous tracer concentration differenceequals the ratio of blood flow to the effective volume oftracer distribution in the Kety-Schmidt method (15, 16).To convert effective volume to muscle mass, it is necessaryto correct for the relative densities of blood and muscleand for the blood-muscle partition coefficient of the tracer.Since both correction factors have values near unity (21-23), no numerical corrections was made. Thus, the formulaused to calculate diaphragmatic blood flow (Q di) wasQ di = 100 X (equilibrium concentration/area), in milli-liters per minute per 100 grams.

The oxygen consumption of the diaphragm was calculatedas the product of diaphragmatic blood flow and arterio-venous difference in oxygen content, using the formula:

Vo2 di = EQdi X (A-V)02 di]/100

where V^02 di and Q di are, respectively, diaphragmaticoxygen consumption and blood flow expressed as millilitersper minute per 100 grams, and (A-V)02 di is diaphragmaticarteriovenous oxygen content difference in ml/100 ml. Bloodoxygen content was measured by the method of Van Slykeand Neill (24).

Diaphragmatic blood flow and oxygen consumption wereconverted to absolute values by multiplying the value per100 g by the weight of the diaphragm. Weight was esti-mated from the highly significant relationship previouslyestablished in the dog (4): diaphragmatic wt in grams =25.09+4.15 body wt in kilograms.

Minute ventilation, cardiac output, and bloodpressureMinute ventilation was measured by attaching the endo-

tracheal tube to a low-resistance, low dead space direc-tional breathing valve connected to a 120-liter Tissot spi-rometer. Minute ventilation was expressed either as liters

1218 D. F. Rochester

body temperature and pressure, saturated with water vapor(BTPS) per minute per kilogram or as liters BTPS perminute. Cardiac output was determined from the femoralarterial blood concentration-time curves inscribed after bolusinjection of indocyanine green dye (25).

Experimental protocolDiaphragmatic blood flow and oxygen consumption were

determined in three experimental conditions: while the ani-mals breathed quietly; during hyperventilation induced byadministration of 5% C02 in 14% or 21%o oxygen; andwhen the diaphragm was not contracting. During the non-contracting periods, the animals were ventilated with avolume respirator (Model 614 Respiration Pump, HarvardApparatus Co., Inc., Millis, Mass.). Diaphragmatic con-traction was abolished either by hyperventilation to thepoint where diaphragmatic electrical activity disappeared,or by administration of a loading dose of 20 mg of suc-cinyl choline followed by a maintenance infusion of 1-2mg/min.

Blood removed for measurement of krypton and dye con-centrations was replaced by an equivalent volume of nor-mal saline to prevent hypovolemia.

RESULTSAnalysis of the xenon levels in blood obtained from theleft inferior phrenic vein, the thoracic portion of the in-ferior vena cava, and from a systemic artery duringinfusion of xenon into the lower inferior vena cavarevealed a consistent picture (Fig. 3). The xenon levelin thoracic inferior vena cava blood rose rapidly to aplateau within two min. Radioactivity in systemic ar-terial blood rose slowly to 12-20% of the thoracic in-ferio'r vena cava level. Radioactivity in phrenic venousblood remained at background levels for i min., thenrose very slowly to about I the systemic arterial level.These results were unaffected by varying the samplingrate in the inferior phrenic vein from 5 to 10 ml/min.

These observations indicate that there is no con-tamination of inferior phrenic venous blood with in-ferior vena cava blood. The only way the tracer reachesinferior phrenic venous blood is through perfusion ofdiaphragm muscle by xenon-labeled systemic arterialblood.

Diaphragm muscle tissue levels of AXe were measuredat necropsy in three dogs. In each animal the cruralmuscle fibers had high levels of radioactivity per milli-gram wet weight, whereas the thin sheets of musclehalfway between central tendon and chest wall containedabout half as much radioactivity per unit weight. Muscleobtained at the junction with the central tendon or thechest wall had intermediate levels of activity. The cen-tral tendon itself contained almost no 1'Xe. When musclestrips were exposed to air, the tissue radioactivity fellto half its original value in about 20 min. This rate istoo slow to explain the differences in levels of radio-activity between the flat muscle sheet and crural por-tion of the diaphragm.

TIVC

FA

LI PV

0 15 30 45 60 75Time, s

FIGuRE 3 The concentrations of AXe in thoracic inferiorcava blood (TIVC), in femoral arterial blood (FA), andleft inferior phrenic venous blood (LIPV) during the first2 min of constant rate infusion of 'Xe in saline into thelower inferior vena cava.

The reproducibility of the methods was evaluatedfrom two consecutive determinations of diaphragmaticblood flow and oxygen consumption made under thesame physiologic conditions of either quiet breathing orhyperventilation. The reproducibility coefficient was cal-culated as the difference between two consecutive de-terminations expressed as a percent of the mean of thetwo determinations. The sign of the difference was ig-nored. For blood flow, the reproducibility coefficientaverage 20±SD 11%; for oxygen consumption it aver-aged 11±SD 6%.

Values of minute ventilation and of diaphragmaticblood flow, arteriovenous oxygen difference, and oxygenconsumption measured in 23 healthy dogs during quietbreathing are summarized in Table I. In the healthyanimals minute ventilation averaged 0.204±SD 0.069liter/min per kg; diaphragmatic blood flow was 22+SD6 ml/min per 100 g; the diaphragmatic arteriovenousoxygen content difference was 6.1 +SD 2.5 ml/100 ml anddiaphragmatic oxygen consumption was 1.2+SD 0.3 ml/min per 100 g. During the control period, diaphragmaticblood flow was significantly dependent on cardiac output(Fig. 4), and the average ratio of diaphragmatic bloodflow to cardiac output was 0.9±SD 0.3%. Neither dia-phragmatic blood flow nor oxygen consumption was sig-nificantly related to minute ventilation during quietbreathing (Fig. 5).

In the animals with pneumonia, minute ventilation,diaphragmatic blood flow, oxygen extraction, and oxygenconsumption were all significantly greater than inhealthy dogs. The increases were roughly proportionalto the gross anatomic extent of lung involvement. Dog21 had scattered small grey infiltrates throughout bothlungs with healthy-looking areas inbetween. Dog 55 hadcongestion and consolidation limited to the posterior


QdimilminilOOg

40r

301-

201

101

.F* 0

*0 0 0

*':*0

0 0

1 t I II I0 50 100 150 200 250

Cardiac output, ml / min kg

FIGURE 4 Diaphragmatic blood flow (Q di) as a functionof cardiac output in healthy dogs at rest. The equation ofthe regression line is y = 13.60 + 0.057 x (n = 29, r=0.499, t= 2.98, P < 0.01).

portions of the right lung. Dog 46 had extensive bi-lateral congestion, edema, and consolidation. Dog 48 as-pirated vomitus before intubation, and at necropsy hadpneumonia involving virtually all of each lung. In con-trast to healthy animals, there was a suggestive correla-tion between diaphragmatic blood flow and minute ven-tilation (n = 4, r = 0.88, t = 2.62, P < 0.1) and thecorrelation between diaphragmatic oxygen consumptionand minute ventilation was significant (n = 4, r = 0.98,t=7.40, P<0.02).

During quiet breathing, diaphragmatic blood flow andthe diaphragmatic arteriovenous oxygen extraction

ml /min 100g

40

0.

0

20 *- 0

A

a

*i

0.4 0.8Vt, liters BTPS

VO2diml min 1100g

4

a

* aA2 . *

00

_ " "I0

0 __ l l ll0

;/min/kg0.4 0.8

FIGURE 5 Diaphragmatic blood flow (Q di) and oxygenconsumption (Vo2 di) as functions of minute ventilation(Vu) during quiet breathing. Data for normal animals aredenoted by the closed circles ( 0), and for dogs withpneumonia by the open triangles (A).

had a reciprocal relationship in healthy dogs (Table I,Fig. 6). The regression equation describing the relation-ship between the reciprocal of the arteriovenous oxygencontent difference and blood flow to the diaphragm was[1/(A-V)Os di] = 0.00877 Q di-0.0015 (n = 23, r =

0.708, t = 4.59, P < 0.001). Since the intercept value isnot significantly different from zero (P < 0.001) it wasignored, and the regression line was replotted as therectangular hyperbola in Fig. 6, which relates the

TABLE IDiaphragmatic Blood Flow (Q di), Arteriovenous Oxygen

Difference [(A- V)02 di], Oxygen Consumption(VW2 di), and Minute Ventilation (f E) in

23 Normal and 4 Sick Dogs duringQuiet Breathing, at Rest

Dog Qdi (A-V)02 di Vo, di

ml/min/100 g Vol % ml/min/100 g

Healthy dogs10 1411 2412 1613 1315 1520 1322 1724 2125 1926 2127 2335 2236 2239 3040 2341 1942 2244 2845 3650 3151 2252 2653 23

Mean 22SD 6

Dogs with21464855

MeanSDtUp

pneumonia21304529

3110

2.70<0.02

5.26.5

10.811.7

8.810.2

5.34.35.07.97.84.54.14.25.56.74.2 -

4.52.64.37.75.63.2

6.12.5

11.810.7

9.68.3

10.11.53.11

<0.01

0.71.51.71.51.31.40.90.90.91.71.81.00.91.21.31.20.91.30.91.41.71.40.7

1.20.3

2.53.24.42.4

3.10.97.80

<0.001

VE

liter BTPS/min/kg

0.1470.3660.1730.2180.2020.1660.1320.1220.0650.1520.2990.3050.2700.1750.2680.1850.2750.1390.2470.2010.2280.1890.178

0.2040.069

0.3910.4470.7160.323

0.4690.1725.64

<0.001


*

TABLE I IDiaphragmatic Blood Flow (Q di), Arteriovenous Oxygen

Difference [(A-V) 02 di], and Oxygen Consumption(Vo2 di) during Quiet Breathing (QB) and

when the Diaphragm is notContracting (NC)

Qdi (A-V) 02 di Vo, diVogdi NC

Dog QB NC QB NC QB NC Vo2 di QB

ml/min/100 g Vol % ml/min/100 g

Healthy dogs35 22 16 4.5 4.9 1.0 0.8 0.836 22 22 4.1 3.3 0.9 0.7 0.852 26 18 5.6 2.1 1.4 0.4 0.356 18 1 1 4.2 3.4 0.8 0.4 0.558 18 21 7.0 3.0 1.2 0.6 0.5

Mean 21 18 5.1 3.3 1.1 0.6 0.6SD 3 4 1.2 1.0 0.2 0.2 0.2f 1.46 2.45 3.58P <0.2 <0.05 <0.01

diaphragmatic arteriovenous oxygen content differenceto diaphragmatic perfusion. The equation of this lineis: (A-V)O di X Q di = 114, which corresponds to adiaphragmatic oxygen consumption of 1.14 ml/min perlOOg.

Total body oxygen consumption was measured in fivedogs. The absolute value of diaphragmatic oxygen con-sumption, obtained as the product of the oxygen con-sumption per 100 g and diaphragmatic weight, aver-aged 1.O+SD 0.2% of total body oxygen consumptionduring quiet breathing.

Diaphragmatic contraction was abolished by succinylcholine in two dogs and by hyperventilation with avolume respirator in three animals. The oxygen con-sumption of the resting diaphragm was 60±SD 20%of the value measured during quiet breathing (TableII). The difference between the levels of diaphragmaticoxygen consumption measured during quiet breathingand when the diaphragm was at rest was significant(t=3.50,P<0.01).

The effects on 16 dogs of breathing 5% COs in either21% or 14% oxygen are shown in Fig. 7. Minute ven-tilation rose significantly (P < 0.001) from an averageof 0.238±SD 0.070 liter/min per kg to an average of0.833±SD 0.361 liter/min per kg. Diaphragmatic bloodflow increased in 14 of the 16 animals. The one dog thathad a fall in blood flow during hyperventilation had anunusually high level of diaphragmatic perfusion duringthe control period. Blood flow averaged 20±SD 5 ml/minper 100 g of diaphragm during quiet breathing, and25+SD 5 ml/100 g during CO2-induced hyperventilation.The increase, though slight, was significant (P < 0.01).The greater diaphragmatic arteriovenous oxygen con-tent difference was also significant (P < 0.01).

(A-V)02 di, volume %

0 10 20 30 40Odi. ml/min!lOOg

FIGURE 6 Diaphragmatic arteriovenous oxygen content dif-ference [(A-V)02di] as a function of diaphragmatic bloodflow (Q di) in healthy dogs at rest. The equation of therectangular hyperbola is: (A-V)02di X Q di'= 114. Seetext for details.

Hyperventilation consistently elevated diaphragmaticoxygen consumption, but to a variable extent (Fig. 7).During quiet breathing these diaphragms utilized 1.2±SD 0.3 ml of 02/min per 100 g. Utilization- rose signifi-

50r-Qdiml/min/lOOg

25

/1,IiI00

I II

-Il

0 0.4 0.8 1.2 1.6VE, liters BTPS/ min /kg

2(A-V)02divolume %

1

VO2diml / min /100g

5.0

2.5

0

FIGURE 7 Diaphragmatic blood flow (Q di), arteriovenousoxygen difference [(A-V)02 di], and oxygen consumption(Vo2 di) as functions of minute ventilation (VE) in 16healthy dogs which inhaled 5% C02 or 5%o C02 and 14%02. The line for each dog connects the points measuredduring quiet breathing and hyperventilation.


TABLE IIIMinute Ventilation, Diaphragmatic Oxygen Consumption

and the Diaphragmatic Oxygen Cost of Breathingduring Quiet Breathing (QB) and

Hyperventilation (HV)

VE V2Odi-VOsdi/VF AVOsdi/AVE

QB HV QB HV QB HV-QB

liters BTPS/min ml/min mi/liter mi/literHealthy dogs

29 6.57 19.80 1.5 2.7 0.23 0.0930 6.08 11.11 1.3 2.3 0.21 0.2031 6.48 17.21 1.5 1.8 0.23 0.0332 4.82 21.98 2.0 3.9 0.41 0.1133 7.04 40.26 1.6 4.5 0.23 0.0934 6.63 26.97 1.3 2.0 0.20 0.0338 5.02 16.33 1.5 2.4 0.30 0.0856 8.82 42.34 1.1 2.5 0.12 0.0457 3.03 11.25 1.0 2.0 0.33 0.0258 4.03 12.73 1.6 3.6 0.40 0.2359 4.58 11.41 1.5 3.6 0.33 0.3160 4.39 13.98 2.0 3.3 0.46 0.1461 5.96 15.36 1.2 2.5 0.20 0.1462 7.75 19.23 1.9 4.6 0.25 0.2486 6.21 19.35 1.9 4.6 0.31 0.2190 4.00 27.49 0.7 2.6 0.17 0.19

Mean 0.27 0.13SD 0.09 0.09t* 4.61P* <0.001

Dogs with pneumonia2 1 10.28 3.4 0.3346 8.53 3.3 0.3948 21.80 6.7 0.3155 10.56 4.4 0.42

Mean 0.36SD 0.05tt 1.81Pt <0.1

* Difference between Vo2 di/VF and A\Vo2 di/AVE in healthy dogs.t Difference between VO2 di/.TE in healthy dogs as compared to dogs withpneumonia.

cantly to 2.3+SD 0.8 ml of 02/min per 100 g duringhyperventilation (P < 0.001).

The relationship between minute ventilation and dia-phragmatic oxygen consumption can be examined ingreater detail by comparing the ratio of the total dia-phragmatic oxygen consumption, expressed in millilitersper minute, to the ventilation measured in liters BTPSper minte. In 16 normal animals, the ratio of diaphrag-matic oxygen consumption to minute ventilation was0.27±0.09 ml/liter during quiet breathing (Table III).Under comparable circumstances, the value of the ratioin the four animals with pneumonia was 0.36±SD 0.05mi/ter (Table III). Although this level of oxygencost was slightly higher than in the healthy dogs, thedifference was not significant (P < 0.1).

When minute ventilation and diaphragmatic oxygenconsumption were increased by means of 5% CO or 5%

CO and 14% 02 inhalation, the ratio of the increment indiaphragmatic oxygen consumption to the increment inminute ventilation averaged 0.13±SD 0.09 ml/liter.This value was significantly lower than the ratio ofdiaphragmatic oxygen consumption to ventilation mea-sured during quiet breathing in the same animals (P <0.001).

DISCUSSIONValidity of the method. The left inferior phrenic

vein with its tributaries is the only major venous drain-age system for the left hemidiaphragm in the dog. Itdoes not anastomose significantly with other regionalvenous systems, including those draining the chest walland the adrenal venous system. Blood can be sampledat 5-10 ml/min from the left inferior phrenic vein with-out contamination from the inferior vena cava.

Perfusion per unit mass of diaphragm was found tobe quite uniform except at the periphery of the venousdrainage area. The bulk of the flat muscle sheet has com-parable radioactivity 3 min after cessation of a satu-rating AXe infusion, whereas there is more radioactivityin areas immediately adjacent to the chest wall andcentral tendon, and in the crural fibers. Since these latterareas represent the end of an essentially nonanastomoticvascular network, it is probable they receive less bloodflow.

It was not possible to sample blood from individualvenous tributaries. Nevertheless, the uniform distributionof radioactivity in the center of the diaphragmatic musclesuggests that blood flow to this area is uniform, andthat use of the Kety-Schmidt method to measure dia-phragmatic muscle blood flow is valid.

The average level of blood flow to the diaphragm,measured during quiet breathing, was 22±SD 6 ml/minper 100 g. This approximately half the level of dia-phragmatic perfusion previously measured in this labora-tory from the clearance of 1'Xe after intramuscular in-jection (4). The difference in estimates might resultfrom several factors. It is possible that the earlierestimate was too high, since analysis of the initial clear-ance rate- of xenon by the method of Lassen, Lindbjerg,and Munck (21, 26) yielded, on the average, a 20%lower blood flow value (4). It is also possible that thepresent estimate of blood flow is too low. No correctionwas made for the transit delay through the samplingcatheter. At most this is i min, which would cause a15% underestimate of blood flow.

Another problem stemming from use of the Kety-Schmidt method to measure diaphragmatic perfusionis related to the equilibrium tracer concentration. Theerror involved is more difficult to evaluate. In thesestudies, equilibrium venous blood krypton concentrationafter 20-30 min of infusion was 20±SD 12% lower than


the simultaneous arterial blood tracer level. Prolongingthe infusion period to 40 min made little difference.In general, the difference between arterial and venousblood tracer levels at the end of the infusion period wasgreater when the diaphragm contracted gently, and lesswhen the diaphragm contracted vigorously.

The reason for the persistant arteriovenous kryptondifference after prolonged infusion is not apparent. Nosignificant loss from the venous sampling catheter wasdetected. It is possible that there was a loss of tracerfrom the diaphragm to adjacent tissue, particularly intothe lung, since Gregg, Longino, Green, and Czerwonkafound large losses of nitrous oxide from the exposedsurface of the heart in an open-chest animal preparation(27). Other investigators have noted a 5-10% differ-ence between arterial and coronary sinus blood indicatorlevels when either krypton or nitrous oxide was used tomeasure myocardial blood flow by the Kety-Schmidtmethod (15, 28-31). Several workers attributed thedifferences to inhomogeneity of blood flow within themyocardium, or to loss into epicardial fat (29-31).

It was not possible to estimate the rate of loss ofkrypton from the perfused living diaphragm. Xenondiffuses very slowly from excised diaphragmatic strips,but the conditions are not comparable to those in per-fused muscle. It must be pointed out that if there werea steady-state loss of tracer from tissue during a con-stant rate saturating infusion, then both tissue and ve-nous blood tracer concentrations should be lower thanarterial blood tracer levels. Further, muscle tissue andmuscle venous blood tracer levels decay at virtually thesame rate after cessation of a prolonged infusion of eitherhydrogen or xenon (19, 20). Therefore, use of the ve-nous tracer level as representative of equilibrium tissuelevel seems justified.

To summarize, blood flow to the diaphragm may havebeen overestimated by 20% when calculated from xenonclearance, and underestimated by 15% when calculatedfrom the equilibrium level and integrated diaphragmaticarteriovenous difference of krypton. The combined effectof these correction factors is to yield quite similar esti-mates of blood flow to the diaphragm from both meth-ods. During quiet breathing, diaphragmatic perfusion inthe dog probably lies around 25 ml/min per 100 g,which is very close to the level of 31 ml/min per 100 gmeasured in the unanesthetized rhesus monkey by theradioactive microsphere method.'

The reproducibility of the present methods of measur-

ing diaphragmatic blood flow and oxygen consumptioncan be compared with estimates of myocardial blood flowand oxygen consumption made by the Kety-Schmidttechnique. When the present reproducibility data were

' Forsyth, R. P. Personal communication.

recalculated according to the formula of Jorgensen,Kitamura, Gobel, Taylor, and Wang (29), the repro-ducibility of the diaphragmatic blood flow measurementwas somewhat poorer, and the reproducibility of dia-phragmatic oxygen consumption was somewhat betterthan the values reported by Jorgensen and his colleaguesfor the myocardium.

The present method of measuring diaphragmatic bloodflow offers several advantages over the xenon clearancemethod. The need for laparotomy to expose the dia-phragm is eliminated, and there is no injection traumato the diaphrgam. Sampling diaphragmatic venous bloodpermits measurement of the diaphragmatic arteriovenousdifference in blood oxygen content, and therefore, cal-culation of diaphragmatic oxygen consumption. Farfewer experiments were lost than with the xenon method.Finally, the scatter of data between animals was muchlower. The standard deviation of diaphragmatic bloodflow measured during quiet breathing was 27% of themean value in the present study, whereas with thexenon clearance method it was 52% of the mean.

Physiological considerations. When the diaphragmcontracts gently to sustain quiet breathing in normoten-sive dogs, the primary determinant of its perfusion isthe level of cardiac output (Fig. 4). These observationsconfirm previous results obtained by the xenon clear-ance method (4). The effect of hypotension on diaphrag-matic blood flow was not studied.

The oxygen utilization of the diaphragm is rather con-stant during quiet breathing (Table I). As with diaphrag-matic blood flow, there is no correlation in the controlperiod between diaphragmatic oxygen consumption andminute ventilation (Fig. 5). The relative constancy ofdiaphragmatic oxygen consumption is independent ofchanges in blood flow. Whenever diaphragmatic bloodflow is unusually high or low for quiet breathing, thereis a reciprocal change in oxygen extraction. Hencea plot of diaphragmatic blood flow and arteriovenousoxygen difference fits a rectangular hyperbola that isan isopleth of diaphragmatic oxygen utilization (Fig. 6).The value of this isopleth, 1.14 ml/min per 100 g, isvery close to the measured average value of 1.2 ml/minper 100 g under control conditions. These data suggesta relative absence of autoregulation of diaphragmaticblood flow during minimal efforts.

Hyperventilation consistently and significantly in-creases diaphragmatic blood flow, arteriovenous oxygendifference, and oxygen consumption, but the changesare not large (Fig. 7). If the average changes are ex-pressed as a percent of control values, then a 100% in-crease in minute ventilation is associated with only a13% increase in blood flow to the diaphragm, and a 19%increase in the diaphragmatic arteriovenous oxygencontent difference. To support this increase in ventila-


tion, diaphragmatic oxygen utilization is augmented by40%.

Oxygen utilization by respiratory muscles is custo-marily related to the level of ventilation by determiningthe amount of oxygen required to provide a liter of ven-tilation. In the method of Liljestrand, oxygen cost iscalculated as the quotient of the increment in whole bodyoxygen consumption caused by hyperventilation, and theincrement in minute ventilation (5). In like fashion,the diaphragmatic oxygen cost of breathing was com-puted from the increments in diaphragmatic oxygenconsumption and minute ventilation. The average valuein anesthetized animals that increased their ventilationsome 240% over controls levels was 0.13±SD 0.09 ml02/liter of ventilation (Table III).

From the formula of Albers, which relates total bodyoxygen consumption to minute ventilation in the dog(12), it can be estimated that 2.5 ml of oxygen arerequired to support a ventilation of 5 liter/min. Hencethe oxygen cost of breathing is 0.5 ml/liter. This is ap-proximately four times larger than the current estimateof the diaphragmatic oxygen cost of breathing. It hasbeen suggested that the apparatus used by Albers had ahigh internal resistance to air flow (13). Another rea-son for the discrepancy may lie in the marked differencesin experimental techniques.

The most important factor in evaluating the relation-ship between minute ventilation and diaphragmatic oxy-gen consumption is the extent to which any level of ven-tilation is supported by inspiratory muscles other thanthe diaphragm. It is generally accepted that the dia-phragm is the major or sole muscle employed duringquiet breathing (32). Fluoroscopic observation re-vealed relatively uniform diaphragmatic excursion whendogs breathed quietly, but this could not quantified.There were no obvious differences in the way the dia-phragms moved in the animals with pneumonia.

It was not possible to assess recruitment of otherinspiratory muscles in this study. In the rabbit extra-diaphragmatic muscles contribute an average of 25%of the tidal volume when tidal volume is maximal duringrebreathing. However, there is considerable variationin individual animals (32). Such variation would helpto explain the large scatter in the estimates of the dia-phragmatic oxygen cost of breathing.

Another cause of scatter in these estimates may bedifferences in airway resistance. Some animals withoutovert pneumonia had much more bronchial secretionthan others.

Despite the variation, it is readily apparent that theincrease in diaphragmatic energy expenditure requiredfor modest levels of hyperventilation is small. For ex-ample, the diaphragm of a typical 20-kg dog weighs 110g. During quiet breathing at 5 liters/min, the diaphragm

would consume about 1.3 ml of oxygen/min. Of this,about 0.8 ml of Os/min is needed for basal metabolism,and 0.5 ml of 02/min is required to support ventilation.The oxygen cost to the diaphragm of quiet breathing is,therefore, 0.5/5 or 0.10 ml/liter. When the animalbreathes at 20 liter/min, the increased ventilation isaccomplished at an oxygen cost to the diaphragm of0.13 ml/liter. Hence the increase in diaphragmatic oxy-gen consumption would be 15 X 0.13 or about 2 ml/min.

The chance occurrence of multilobar pneumonia infour dogs provided some insight on the effect of a re-strictive pulmonary disease on the energetics of thediaphragm. At the same level of anesthesia as used fornormal animals, the sick dogs hyperventilated (Table I).Their diaphragmatic blood flow and oxygen consumptionwere also above normal (Table I), and tended to beproportional to the increased ventilation (Fig. 4). Theoxygen cost of increasing ventilation was not measuredin these animals, but the ratio of diaphragmatic oxygenconsumption to minute ventilation during the controlperiod was not significantly different from the ratiofound in healthy animals (Table III).

This unexpected result makes it appear that it is al-most as easy to ventilate stiff lungs as it is to ventilatenormal lungs. The following example indicates otherwise.A typical sick dog weighing 20 kg breathes 10 liter/min, and its- diaphragm consumes 3.3 ml of oxygen/min. If the basal metabolism of the diaphragm is normal,then about 2.5 ml of oxygen are expended to support theminute ventilation. Thus, the diaphragmatic oxygen costof breathing is 2.5/10 or 0.25 ml/liter. Pneumonia in-creases diaphragmatic oxygen consumption through twomechanisms. First is the increase in minute ventilationper se, and second is the two- to threefold increase inthe energy required for each liter of ventilation.

ACKNOWLEDGMENTSThis study was supported by a grant from the New YorkHeart Association and by grants HE-02001, HE-05741,and HE-05443 from the National Institutes of Health.

REFERENCES1. Anrep, G. V., S. Cerqua, and A. Samaan. 1933-34. The

effect of muscular contraction upon the blood flow inthe skeletal muscle, in the diaphragm, and in the smallintestine. Proc. R. Soc. Lond. B. Biol. Sci. 114: 245.

2. Mott, J. C. 1953. The circulation of the thoracic cagein the dog and its reaction to haemorrhage. J. Physiol.(Lond.). 121: 80.

3. Forsyth, R. P., B. I. Hoffbrand, and K. L. Melmon.1970. Redistribution of cardiac output during hemor-rhage in the unanesthetized monkey. Circ. Res. 27:311.

4. Rochester, D. F., and M. Pradel-Guena. 1973. Measure-ment of diaphragmatic blood flow in dogs from xenon'mclearance. J. Appl. Physiol. 34: 68.


5. Liljestrand, G. 1918. Untersuchungen uiber Atmungsar-beit. Skand. Arch. Physiol. 35: 199.

6. Cournand, A., and D. W. Richards, Jr. 1954. The oxy-gen cost of breathing. Trans. Assoc. Am. PhysiciansPhila. 67: 162.

7. McKerrow, C. B., and A. B., Otis. 1956. Oxygen costof hyperventilation. J. Appl. Physiol. 9: 375.

8. Campbell, E. J. M., E. K Westlake, and R. M. Cher-niack 1957. Simple methods of estimating oxygen con-sumption and efficiency of the muscles of breathing.J. Appl. Physiol. 11: 303.

9. Bartlett, R. G., Jr., H. F. Brubach, and H. Specht.1958. Oxygen cost of breathing. J. Appl. Physiol. 12:413.

10. Cherniack, R. M. 1959. The oxygen consumption andefficiency of the respiratory muscles in health and em-physema. J. Clin. Invest. 38: 494.

11. Fritts, H. W., Jr., J. Filler, A. P. Fishman, and A.Cournand. 1959. The efficiency of ventilation duringvoluntary hyperpnea: studies in normal subjects andin dyspneic patients with either chronic pulmonaryemphysema or obestiy. J. Clin. Invest. 38: 1339.

12. Albers, C. 1961. Der Mechanismus des Warmehechelnsbeim Hund. II. Der respiratorische Stoffwechsel warh-rend des Wdrmehechelns. (The mechanism of thermalstress in the dog. II. Metabolism during thermal stress.)Pfluigers Arch. ges. Physiol. 274: 148.

13. Spaich, P., W. Usinger, and C. Albers. 1968. Oxygencost of panting in anesthetized dogs. Respir. Physiol.5: 302.

14. Rochester, D. F. 1970. Measurement of diaphragmaticblood flow and oxygen consumption in the dog. J. Clin.Invest. 49: 80a.

15. Kety, S. S., and C. F. Schmidt. 1945. The determina-tion of cerebral blood flow in man by the use of nitrousoxide in low concentrations. Am. J. Physiol. 143: 53.

16. Kety, S. S., and C. F. Schmidt. 1948. The nitrous oxidemethod for the quantitative determination of cerebralblood flow in man: theory, procedure, and normal val-ues. J. Clin. Invest. 27: 476.

17. Hansen, A. T., B. F. Haxholdt, E. Husfeldt, N. A.Lassen, 0. Munck, H. R. Sorensen, and K Winkler.1956. Measurement of coronary blood flow and cardiacefficiency in hypothermia by use of radioactive kryp-ton-85. Scand. J. Clin. Lab. Invest. 8: 182.

18. Hardewig, A., D. F. Rochester, and W. A. Briscoe.1960. Measurement of solubility coefficient of kryptonin water, plasma and human blood, using radioactiveKrTM. J. Appl. Physiol. 15: 723.

19. Sejrsen, P., and K. H. Tonnesen. 1968. Inert gas dif-fusion method for measurement of blood flow usingsaturation techniques. Comparison with directly mea-

sured blood flow in the isolated gastrocnemius muscleof the cat. Circ. Res. 22: 679.

20. Aukland, K., B. F. Bower, and R. W. Berliner. 1964.Measurement of local blood flow with hydrogen gas.Circ. Res. 14: 164.

21. Lassen, N. A., I. F. Lindbjerg, and 0. Munck. 1964.Measurement of blood-flow through skeletal muscle byintramuscular injection of xenon-133. Lancet. 1: 686.

22. Holzman, G. B., H. N. Wagner, Jr., M. Iio, D. Rabin-owitz, and K. L. Zierler. 1964. Measurement of muscleblood flow in the human forearm with radioactivekrypton and xenon. Circulation. 30: 27.

23. Yeh, S-Y., and R. E. Petersen. 1965. Solubility ofkrypton and xenon in blood, protein solutions, and tissuehomogenates. J. Appl. Physiol. 20: 1041.

24. Van Slyke, D. D., and J. M. Neill. 1924. The deter-mination of gases in blood and other solutions byvacuum extraction and manometric measurement. I.J. Biol. Chem. 61: 523.

25. Caldwell, P. R. B., U. Echeverri, M. M. Kilcoyne, andH. W. Fritts, Jr. 1970. Observations on a model ofproliferative lung disease. II. Description of pulmonarygas exchange and comparison of Fick and dye cardiacoutputs. J. Clin. Invest. 49: 1311.

26. Lassen, N. A. 1964. Muscle blood flow in normal manand in patients with intermittant claudication evaluatedby simultaneous Xe6 and Na' clearances. J. Clin. In-vest. 73: 1805.

27. Gregg, D. E., F. H. Longino, P. A. Green, and L. J.Czerwonka. 1951. A comparison of coronary flow de-termined by the nitrous oxide method and by a directmethod using the rotameter. Circulation. 3: 89.

28. Hedworth-Whitty, R. B., E. Housley, and A. S. Abra-ham. 1969. An improved technique for measuringchanges in myocardial perfusion by the nitrous oxidemethod. Cardiovasc. Res. 3: 496.

29. Jorgensen, C. R., K Kitamura, F. L. Gobel, H. L.Taylor, and Y. Wang. 1971. Long-term precision ofthe N20 method for coronary flow during heavy up-right exercise. J. Appl. Physiol. 30: 338.

30. Klocke, F. J., D. R. Rosing, and D. E. Pittman. 1969.Inert gas measurements of coronary blood flow. Am.J. Cardiol. 23: 548.

31. Eckenhoff, J. E., J. H. Hafkenschiel, M. H. Harmel,W. T. Goodale, M. Lubin, R. J. Bing, and S. S. Kety.1948. Measurement of coronary blood flow by the nit-rous oxide method. Am. J. Physiol. 152: 356.

32. Mognoni, P., F. Saibene, and G. Sant 'Ambrogio. 1969.Contribution of the diaphragm and other inspiratorymuscles to different levels of tidal volumes and staticinspiratory effort in the rabbit. J. Physiol. 202: 517.


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