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R S Kronenberg

Publications and source records attributed to R S Kronenberg.

52 records · Page 3Linked to original sources
PubMed1973

Attenuation of the ventilatory and heart rate responses to hypoxia and hypercapnia with aging in normal men.

The response of ventilation and of heart rate to hypoxia and hypercapnia was determined in eight young normal men age 22-30 yr and eight elderly men age 64-73. The elderly men were selected and carefully screened to eliminate the possibility of cardiopulmonary disease. All the subjects were born at low altitude and had no significant prior exposure to hypoxia. The ventilatory response to hypoxia was measured as the exponential slope constant. k, of regression lines relating the logarithm of incremental ventilation to PAo(2) during isocapnic progressive hypoxia. The heart rate response to hypoxia was measured as the percentage change in heart rate between PAo(2) = 100 and PAo(2) = 40 mm Hg. The ventilatory response to hypercapnia was measured as the slope of regression lines relating ventilation to PAco(2) during rebreathing with PAo(2) > 200 mm Hg. The heart rate response to hypercapnia was measured as the percentage change in heart rate between control values at the start of the rebreathing test and PACO(2) = 55 mm Hg. The ventilatory and heart rate responses to both hypoxia and hypercapnia were significantly decreased in the elderly men as compared to the young men. Hypoxic ventilatory drive was decreased by 51+/-6% (mean +/-SEM: P < 0.001) and hypercapnic drive by 41+/-7% (P < 0.025). The percentage change in heart rate produced by hypoxia was 34+/-5% (mean +/-SEM) in the young normals and 12+/-2% in the old normals (P < 0.005). Similar figures for heart rate in response to hypercapnia were 15+/-3% and -1+/-1% for the young and old normal groups (P < 0.001). We conclude that ventilatory and heart rate responses to hypoxia and hypercapnia diminish with age. These alterations in both ventilatory and circulatory controls could make older individuals more vulnerable to hypoxic disease states.

Adult↗
PubMed1971

Pulmonary artery pressure and alveolar gas exchange in man during acclimatization to 12,470 ft.

Pulmonary hemodynamics and gas exchange were studied in four physicians during 72 hr acclimatization to 12,470 ft. Pulmonary catheters were left in three subjects for 72 hr. Resting mean pulmonary arterial pressure (PAP) rose progressively during the first 24 hr from 10.3 +/-1.0 to 21.1 +/-4.0 torr and remained at this level. During this same 24 hr period cardiac output increased from 7.1 +/-1.4 to 8.4 +/-2.0 liters/min and total pulmonary resistance rose from 122 +/-16 to 209 +/-40 dynes.sec/cm(-5). Excercise at 60 w after 24 hr of hypoxia increased PAP to 28.8 +/-5.1 torr and decreased total pulmonary resistance to 155 +/-25. Shunt fractions were 11 +/-3.8% after 24 hr at altitude and fell to 7 +/-0% after 72 hr. Alveolar to arterial O(2) difference (P(A-a)(O2)) breathing oxygen fell from 116 +/-10.8 to 92 +/-33.3 torr during the same period of acclimatization, whereas dead space to tidal volume ratio (V(D)/V(T)) rose from 33 +/-4.0% to 40 +/-5.3% and P(A-a)(O2) breathing ambient air rose from 8 +/-2.6 to 11 +/-3.0 torr. Inspiratory static lung compliance decreased significantly from a control of 176 +/-8 to 141 +/-8 ml/cm H(2)O after 72 hr of hypoxia. After 4-7 days at altitude, further deterioration in gas exchange was observed after a 5 mile, 1800 ft climb to the summit (14,255 ft) and return. P(A-a)(O2) on air rose from 2.5 +/-2.1 just before starting, to 16.3 +/-2.8 at the summit (rested), and was still 9.0 +/-2.2 several hours after returning. The O(2)-breathing values paralleled these, whereas dead space appeared to fall. We speculate that the hypoxic pulmonary hypertension which develops over 24 hr in some way may be responsible for a reduction of compliance and deterioration in oxygen exchange efficiency, possibly representing a sub-clinical form of pulmonary edema of high altitude. The increased alveolar to arterial O(2) difference induced by hypoxic exercise persists for several hours of hypoxic rest.

Acclimatization↗