[Education of respiratory physiology in 2nd-year medicine: current challenges].

The author describes some of the challenges which face present day teaching in respiratory physiology. These are 1. poor integration with basic science, 2.

Oxygen supply and uptake in tissue models with unequal distribution of blood flow and shunt.

The effects of unequal distribution of blood flow on O2 uptake are studied on a model composed of 3 tissues compartments with blood flow/O2 requirement ratios in the relation 9:3:1 (unequal blood flow model), a model with 33% shunt blood flow (shunt model), and a single compartment model without shunt (reference model). Diffusion limitation is assumed to be absent. Total blood flow (Q), arterial O2 content (CaO2) and O2 requirement of tissue are varied singly, and the resulting (mixed) venous O2 content (CvO2) and O2 uptake are calculated.

The effect of carbon monoxide on respiration.

In this review the effects of carbon monoxide on tissular oxygenation, at doses which are compatible with life, are considered. In a first section the relative CO-O2 affinity (M*) of various O2 carrying proteins is compared; M* is about 220 for hemoglobin, 20-25 for myoglobin and close to unity for cytochrome oxidases. Thus most of the acute CO toxicity should not be considered as due to malfunction of the intracellular respiratory chain.

Muscle maximal O2 uptake at constant O2 delivery with and without CO in the blood.

In the present study we investigated the effects of carboxyhemoglobinemia (HbCO) on muscle maximal O2 uptake (VO2max) during hypoxia. O2 uptake (VO2) was measured in isolated in situ canine gastrocnemius (n = 12) working maximally (isometric twitch contractions at 5 Hz for 3 min). The muscles were pump perfused at identical blood flow, arterial PO2 (PaO2) and total hemoglobin concentration [( Hb]) with blood containing either 1% (control) or 30% HbCO.

Experimental support for the theory of diffusion limitation of maximum oxygen uptake.

The four experiments summarized above demonstrate that there is a strong relationship between both measured muscle venous PO2 and calculated mean muscle capillary PO2 and VO2max. This is true for whole body or exercising muscle VO2max, and is seen both in isolated canine gastrocnemius and intact man. This behavior is exactly what would be expected if the diffusing properties for oxygen in skeletal muscle play a constraining role in setting maximum VO2.

Effects of altitude acclimatization on pulmonary gas exchange during exercise.

Pulmonary gas exchange was studied in eight normal subjects both before and after 2 wk of altitude acclimatization at 3,800 m (12,470 ft, barometric pressure = 484 Torr). Respiratory and multiple inert gas tensions, ventilation, cardiac output (Q), and hemoglobin concentration were measured at rest and during three levels of constant-load cycle exercise during both normoxia [inspired PO2 (PIO2) = 148 Torr] and normobaric hypoxia (PIO2 = 91 Torr). After acclimatization, the measured alveolar-arterial PO2 difference (A-aPO2) for any given work rate decreased (P less than 0.

Evidence for tissue diffusion limitation of VO2max in normal humans.

We recently found [at approximately 90% maximal O2 consumption (VO2max)] that as inspiratory PO2 (PIO2) was reduced, VO2 and mixed venous PO2 (PVO2) fell together along a straight line through the origin, suggesting tissue diffusion limitation of VO2max. To extend these observations to VO2max and directly examine effluent venous blood from muscle, six normal men cycled at VO2max while breathing air, 15% O2 and 12% O2 in random order on a single day. From femoral venous, mixed venous, and radial arterial samples, we measured PO2, PCO2, pH, and lactate and computed mean muscle capillary PO2 by Bohr integration between arterial (PaO2) and femoral venous PO2 (PfvO2).

Alveolar-arterial equilibration in the lung of sheep.

In order to compare the efficiency of sheep lung with that of dog, gaseous exchange in hypoxia (FIO2 0.12-0.13) with and without CO in the inspired air ( FICO 0.

Simultaneous O2 and CO diffusing capacity estimates from assumed lognormal VA, Q and DL distributions.

O2 and CO pulmonary transfer data obtained in dogs under steady-state conditions in hypoxia by Savoy et al. (Respir. Physiol.

A model for the study of diffusion and perfusion limitation.

On the basis of a very simple model for the association of diffusion and perfusion, an association common to many respiratory gas transfers, a simple equation is described that defines gas partial pressure equilibration in diffusion-perfusion-limited systems as a function of the ratio of D to beta bQ(D = diffusing capacity, beta b = blood capacitance coefficient, Q = perfusion). The equation applies to steady-state conditions and assumes D, beta b, and Q to be independent of gas partial pressures. In spite of the fact that this assumption may represent a gross simplification, the equation can be regarded as a powerful conceptual tool in the analysis of most gas exchange systems.

[Simultaneous measurement of blood concentrations of O2 and CO with a Van Slyke apparatus].

imultaneous analysis of a blood sample for its O2 and CO contents (Co2 and Cco) with the original manometric technique of Van Slyke entails a directional error on Co2 and Cco when blood contains CO. This important drawback is due to the fact that Na2S2O4 employed for the O2 absorption also reduces methemoglobin into hemoglobin which then reabsorbs a variable amount of the extracted CO. This amount is equal to the directional error and results in an overestimation of Co2 and in an underestimation of Cco.

Volume flow, hydraulic conductivity and electrical properties across bovine tracheal epithelium in vitro: effect of histamine.

Volume flow (Jv), potential difference (delta psi), short-circuit current (io) and electrical resistance (R) were measured simultaneously across bovine tracheal epithelium in vitro. Under basal conditions, with no applied hydrostatic or osmotic pressure gradients (delta P = 0, delta phi = 0), no spontaneous Jv was observed. delta psi was 31 +/- 2 mV (lumen negative ), io 161 +/- 8 microA cm-2 and R 202 +/- 9 omega cm2, n = 50.

Comparison of steady state pulmonary diffusing capacity estimates for O2 and CO in dogs.

In view of the fact that the inhomogeneity effects on pulmonary diffusing capacity (DL) estimates are quite different for O2 and for CO, simultaneous determinations of steady-state DLCO and DLO2 were attempted and compared. To this end, pulmonary gas exchange was measured in 17 anesthetized and artificially ventilated dogs, in hypoxia with and without carbon monoxide in inspired gas (FIO2 = 0.12, FICO = 0.

Pulmonary O2 diffusing capacity estimates from assumed log-normal VA/Q distributions.

Steady-state pulmonary gas exchange has been measured in hypoxia in 33 mongrel dogs with the aim of comparing DLO2 estimates obtained with three procedures differing by the models assumed for functional inhomogeneity. In the first procedure the lung was assumed to be homogeneous and the corresponding DLO2 estimate was 15 mumol . min-1.