A B S T R A C T Pulmonary hemodynamics and Rotta, Canepa, Hurtado, Velasquez, and Chavez in 1956 (1) and has been confirmed many times since, both in acclimatized natives (2, 3) and in newcomers (4). The relationship of this pulmonary hypertension to the development of high altitude pulmonary edema (HAPE) is uncertain, but pulmonary artery pressure is higher during episodes of HAPE than during control observations in the same individuals (5), and persons who have had such episodes previously have higher pulmonary artery pressures when reexposed to altitude than nonsusceptible individuals under the same conditions (6). Although it is recognized that the peak incidence of HAPE occurs 1-3 days after entry to high altitude (7), it has not been established whether pulmonary arterial pressure rises in a progressive fashion over the same time course. A progressive rise in pulmonary arterial pressure during a 6 wk period at 12,700 ft has been reported in steers, apparently associated with the right heart failure termed "brisket disease" (8), but was not observed in lambs in a matched experiment (9). Therefore, we decided to investigate in ourselves the time course of the pulmonary arterial pressure both at rest and during exercise at 12,470 ft and to examine other aspects of cardiovascular function over the same time span. We also explored the possibility suggested by Haab, Held, Ernst, and Farhi (10) and Reeves, Halpin, Cohn, and Daoud (11) that hypoxia widens the alveolar to arterial 02 difference.

Cardiac output (CO) can be determined using pulmonary artery catheters and thermodilution techniques. The purpose of this paper is to describe the thermodilution principle and to consider factors and pathology which may invalidate the CO determination. Thermodilution techniqueThe injection of a known amount of indicator (a cool solution) into the right atrium through the proximal port of a pulmonary artery catheter (PAC) is detected distally by a thermistor located 4 cm from the end of the PAC. ~ The change in temperature of blood in pulmonary artery causes a change in the thermistor Wheatstone bridge resistance which allows a computer to calculate the area under the thermodilution curve (Figure (a)). This and the volume of injectate allow computation of CO. 2 The shape of the thermodilution curve is similar to dye dilution curves except thermodilution recirculation is small (about four per cent of the peak of the curve). 3 The thermodilution curve peaks rapidly and then follows an exponential decay, until there is recirculation or delayed cooling from the residual indicator in the PAC. 4 This last portion of the curve should not be used in determining the area under the curve.Cardiac output is determined from the following equation 2 CO = Vt (TB --Ti)KtK2/ATB(t)dt where Vj is the injectate volume, TB is the blood From the

Extravascular thermal volume of the lung (ETVL) is a double indicator dilution technique of use in measuring pulmonary edema. ETVL and lung mechanics measurements were followed to find a less invasive monitor of pulmonary edema than the double indicator dilution technique. Pulmonary edema was induced by overloading the dogs' circulation with dextran. Phases of overload were defined on the basis of a previous electron microscopic study (Noble et al., Can. Anesthetists Soc. J. 21:275, 1974) of lung biopsies relating anatomic changes to physiologic measurements of ETVL and central blood volume (CBV). Congestion occurred when CBV was elevated and ETVL was not, interstitial edema when ETVL was elevated but smaller than 60% above control and alveolar edema when ETVL greater than 85% above control. Once the dogs were in alveolar edema, they were mechanically ventilated with 4, 8, 12, and 16 cmH2O end-tidal pressure (CPPV). Mean functional residual capacity (FRC) for all 15 dogs did not change up to the time CPPV was applied. Pulmonary resistance did not rise until alveolar edema was present. Once in pulmonary edema, lung compliance always fell as lung water increased. In individual dogs, the compliance fall was directly proportional to the rising lung water. However, the variations in slope and beginning point among dogs made it difficult to predict the amount of lung water from dynamic compliance values. PaO2 fell markedly in alveolar edema as a result of a widened A-a gradient. CPPV did not decrease lung water but did increase FRC and PaO2.

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