PubMed Health⌕ Search

Biomedical subjects

K H Maret

Publications and source records attributed to K H Maret.

8 recordsLinked to original sources
PubMed1986

Nocturnal periodic breathing at altitudes of 6,300 and 8,050 m.

Nocturnal periodic breathing was studied in eight well-acclimatized subjects living at an altitude of 6,300 m [barometric pressure (PB) 350-352 Torr] for 3-5 wk and in four subjects during one night at 8,050 m altitude (PB 281-285 Torr). The measurements at 6,300 m included tidal volume by inductance plethysmography, arterial O2 saturation by ear oximetry (calibrated by arterial blood samples), electrocardiogram (ECG), and electrooculogram. At 8,050 m, periodic breathing was inferred from the cyclical variation in heart rate obtained from a night-long ECG record. All subjects at 6,300 m altitude showed well-marked periodic breathing with apneic periods. Cycle length averaged 20.5 s with 7.9 s apnea. Minimal arterial O2 saturation averaged 63.4% corresponding to a PO2 of approximately 33 Torr, i.e., approximately 6 Torr lower than the normal value at rest during daytime. This was probably the most severe hypoxemia of the 24-h period. At 8,050 m altitude, the cycle length averaged 15.4 s, much longer than predicted by a theoretical model. Cyclical variations in heart rate caused by periodic breathing occurred in all subjects, but abnormal cardiac rhythms such as ventricular premature contractions were uncommon. The severe arterial hypoxemia caused by periodic breathing may be an important determinant of tolerance to these great altitudes.

Adult↗
PubMed1984

Automatic mechanical alveolar gas sampler for multiple-sample collection in field.

A mechanical alveolar gas sampler using the revolver principle capable of collecting six individual expired gas samples is described. The 0.91-kg sampler collects 19-ml samples in pre-evacuated aluminum ampoules equipped with spring-loaded valves from a sampling chamber equipped with two removable one-way valves. On depression of external handles, one of six ampoules located in a removable cartridge is aligned and advanced into the sampling chamber where its valve is opened and then closed. Releasing the handles removes the ampoule from the sampling chamber and automatically rotates the cartridge through 60 degrees to position a new ampoule in preparation for the next sampling sequence. A lock-out mechanism prevents reexposure of any of the ampoules after six samples have been taken. The performance of the sampler is described including its successful use in the field to collect alveolar gas samples on the summit of Mount Everest.

Altitude↗
PubMed1984

Relationship of hypoxic ventilatory response to exercise performance on Mount Everest.

At very high altitude, exercise performance in the human sojourner may depend on a sufficient hypoxic ventilatory response (HVR). To study the relationship of HVR to exercise performance at high altitude, we studied HVR at sea level and 5,400 m and exercise ventilation at sea level, 5,400 m, and 6,300 m in nine members of the American Medical Research Expedition to Everest. The relationship of HVR between individuals was maintained when HVR was repeated after acclimatization to 5,400 m (P less than 0.05). There was a significant correlation in all subjects between HVR and ventilatory equivalent during exercise at sea level (r = 0.704, P less than 0.05). Subjects were then grouped into high (H) and low (L) HVR responders (ventilation increase to end-tidal PO2 of 40 Torr = 21.2 +/- 5.4 and 5.6 +/- 0.9 1 X min-1, respectively. At low and moderate levels of exercise, ventilation at sea level and after acclimatization to 6,300 m was higher in the high HVR group. At 6,300 m blood O2 saturation (Sao2%) decreased from rest to maximum exercise: H = 8.3 +/- 1.8%, L = 20.0 +/- 2.5% (P less than 0.01). HVR correlated inversely in all subjects with the decrease in Sao2 from rest to maximum exercise (P less than 0.05). Climbers with the highest HVR values reached and slept at higher altitudes. We conclude that the relative value of HVR in our group of climbers was not significantly altered after acclimatization; HVR predicts exercise ventilation at sea level and high altitude; the drop in Sao2% that occurs with exercise is inversely related to HVR; and sojourners with high HVR may perform better at extreme altitude.

Altitude↗
PubMed1983

Barometric pressures at extreme altitudes on Mt. Everest: physiological significance.

Barometric pressures were measured on Mt. Everest from altitudes of 5,400 (base camp) to 8,848 m (summit) during the American Medical Research Expedition to Everest. Measurements at 5,400 m were made with a mercury barometer, and above this most of the pressures were obtained with an accurate crystal-sensor barometer. The mean daily pressures were 400.4 +/- 2.7 (SD) Torr (n = 35) at 5,400 m, 351.0 +/- 1.0 Torr (n = 16) at 6,300 m, 283.6 +/- 1.5 Torr (n = 6) at 8,050 m, and 253.0 Torr (n = 1) at 8,848 m. All these pressures are considerably higher than those predicted from the ICAO Standard Atmosphere. The chief reason is that pressures at altitudes between 2 and 16 km are latitude dependent, being higher near the equator because of the large mass of cold air in the stratosphere of that region. Data from weather balloons show that the pressure at the altitude of the summit of Mt. Everest varies considerably with season, being about 11.5 Torr higher in midsummer than in midwinter. Although the mountain has been climbed without supplementary O2, the very low O2 partial pressure at the summit means that it is at the limit of man's tolerance, and even day-by-day variations in barometric pressure apparently affect maximal O2 uptake.

Altitude↗
PubMed1983

Pulmonary gas exchange on the summit of Mount Everest.

Pulmonary gas exchange was studied on members of the American Medical Research Expedition to Everest at altitudes of 8,050 m (barometric pressure 284 Torr), 8,400 m (267 Torr) and 8,848 m (summit of Mt. Everest, 253 Torr). Thirty-four valid alveolar gas samples were taken using a special automatic sampler including 4 samples on the summit. Venous blood was collected from two subjects at an altitude of 8,050 m on the morning after their successful summit climb. Alveolar CO2 partial pressure (PCO2) fell approximately linearly with decreasing barometric pressure to a value of 7.5 Torr on the summit. For a respiratory exchange ratio of 0.85, this gave an alveolar O2 partial pressure (PO2) of 35 Torr. In two subjects who reached the summit, the mean base excess at 8,050 m was -7.2 meq/l, and assuming the same value on the previous day, the arterial pH on the summit was over 7.7. Arterial PO2 was calculated from changes along the pulmonary capillary to be 28 Torr. In spite of the severe arterial hypoxemia, high pH, and extremely low PCO2, subjects on the summit were able to perform simple tasks. The results allow us to construct for the first time an integrated picture of human gas exchange at the highest point on earth.

Acid-Base Equilibrium↗
PubMed1983

Maximal exercise at extreme altitudes on Mount Everest.

Maximal exercise at extreme altitudes was studied during the course of the American Medical Research Expedition to Everest. Measurements were carried out at sea level [inspired O2 partial pressure (PO2) 147 Torr], 6,300 m during air breathing (inspired PO2 64 Torr), 6,300 m during 16% O2 breathing (inspired PO2 49 Torr), and 6,300 m during 14% O2 breathing (inspired PO2 43 Torr). The last PO2 is equivalent to that on the summit of Mt. Everest. All the 6,300 m studies were carried out in a warm well-equipped laboratory on well-acclimatized subjects. Maximal O2 uptake fell dramatically as the inspired PO2 was reduced to very low levels. However, two subjects were able to reach an O2 uptake of 1 l/min at the lowest inspired PO2. Arterial O2 saturations fell markedly and alveolar-arterial PO2 differences increased as the work rate was raised at high altitude, indicating diffusion limitation of O2 transfer. Maximal exercise ventilations exceeded 200 l/min at 6,300 m during air breathing but fell considerably at the lowest values of inspired PO2. Alveolar CO2 partial pressure was reduced to 7-8 Torr in one subject at the lowest inspired PO2, and the same value was obtained from alveolar gas samples taken by him at rest on the summit. The results help to explain how man can reach the highest point on earth while breathing ambient air.

Adult↗
PubMed1980

Reappraisal of extravascular lung thermal volume as a measure of pulmonary edema.

Previous papers have evaluated extravascular thermal volume of the lung (ETVL) as a measure of lung water by using median transit time (tmed) rather than the correct mean transit time (tmean). Calculation of ETVL using tmean (ETVLmean) and tmed (ETVLmed) gave an excellent relationship, ETVLmean = 1.48 ETVLmed - 0.74 (r = 0.99). This allowed us to calculate a new ratio of ETVLmean to PETW = 1.55 +/- 0.17, WHERE PETW is the postmortem value of pulmonary extravascular tissue weight. Thermistors were placed in dogs to determine the contribution of chest wall, pleural and pericardial fluid, left heart, bronchi, and lung gas to the ETVL measurement. We found ETVLmean greater than PETW because of thermal distributioninto left heart (18 +/- 2% of ETVL), bronchi (estimate 7% of ETVL), pulmonary arteries and veins (estimate 7% of ETVL), and perhaps a small portion of chest wall. We could not detect any portion of lung gas or pleural or pericardial effusions as a part of the ETVL measurement. When the distribution into left heart, bronchi, pulmonary arteries, and veins is removed ETVLmean/PETW = 1.07.

Animals↗