Response of pulmonary blood volume to 64 to 114 weeks of intermittent stay at high altitudes

Pulmonary gas exchange in nonnative residents of high altitude

This study represented an initial attempt, by means of cross-sectional investigation, to determine the effects of chronic exposure to high altitude on pulmonary gas exchange. Single-breath D(Lco) and its components were determined at rest and during muscular work in two groups of healthy, non-smoking, sea level natives who had initiated 1-16 yr of residence at 3,100 m altitude either during physical maturation (at age 10+/-4 yr) or as adults (at age 26+/-4 yr). The relative degree of acclimatization achieved in these lowland residents was assessed through their comparison both with normal sea-level values and with two additional groups of short-term sojourners and natives to 3.100 m. D(Lco) at rest and work was significantly elevated above normal and above sojourner values in both groups of resident lowlanders at 3,100 m. The high D(Lco) in the native to 3,100 m was closely approximated in the younger resident lowlander at rest, but only during exercise in the adult resident lowlander. The high D(Lco) at rest and during exercise in the resident lowlanders was not attributable to differences in Hb concentration or in alveolar lung volume: and was accompanied primarily by an increased estimated Dm(co) and to a lesser extent by an expanded Vc. The interpretation and implications of these findings were limited by the low quantitative capability of Vc and Dm(co) estimates and by the cross-sectional nature of the study. Nevertheless, the higher than normal D(Lco) and Dm(co) in the non-native, long-term resident of 3,100 m was substantial, highly significant statistically, and consistent over a wide range of metabolic rates at rest and work. These data provide, then, a reasonable rationale upon which longitudinal experiments may be based to determine the true effects of chronic hypoxia on pulmonary gas exchange in man.

Increased cardiac output as a contributory factor in experimental renal hypertension in dogs

It has been suggested, but not established, that renal hypertension is initiated by increase incardiac output. Recent refinements in electromagnetic flowmeter technology allowed a critical reevaluation of this possibility. Flowmeters were implanted around dogs' ascending aortas and arterial catheters inserted; measurements were made daily before and after production of hypertension by the cellophane perinephritis method. Eight to 15 days after wrapping one kidney in cellophane, with the opposite kidney untouched, group averages for both stroke volume and cardiac output rose significantly (P < 0.005) though there was no change in arterial pressure. Both heart rate and peripheral resistance decreased slightly. Following these measurements, the contralateral normal kidney was removed and measurements were recommenced 24 hours later. After 4 to 7 days, mean arterial pressure rose progressively in all dogs, reaching a plateau 77 ± 8 (SE) mm Hg above control after 14 to 25 days. Hypertension was associated initially with further rise in both stroke volume and cardiac output, and peripheral resistance now became elevated. Four weeks after nephrectomy, peripheral resistance progressively became the predominant cause of elevated pressure while cardiac output returned toward control values. Absence of change in plasma volume and increase in mean circulatory pressure measured in a separate series of 7 dogs suggest that the initial increase in cardiac output preceding rise in pressure was due to enhanced venous return consequent to constriction of capacitance vessels. We conclude that increased cardiac output probably has a contributory role in the development of renal hypertension.

Effect of frusemide on pulmonary blood volume

Intracardiac frusemide given to seven patients recovering from high-altitude pulmonary oedema caused a significant reduction in the pulmonary blood volume before the onset of diuresis. This supports the suggestion that the mobilization of fluid from the pulmonary circuit is responsible for the relief of symptoms in some patients with pulmonary oedema even when a diuresis does not occur.