Desensitization Theory Summary Video
Anxiety, Systematic Desensitization and Graded Exposure Desensitization Theory Summary
Skeletal muscle blood flow is reduced during submaximal Welch et al. Skeletal muscle is not the only organ to which the blood flow is altered by changes in CaO2: blood flow to the heart Hilton and Eichholtz, ; Baron et al.
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Maximal cardiac function is reduced during chronic hypobaric hypoxia, with a reduction in both maximal heart rate fhmax and maximal Desensitizwtion volume VSmax Vogel et al. Reeves and colleagues Reeves et Theorry. However, the point is that the proportional reduction in stroke volume and atrial filling pressure indicates that the heart was not ischaemic and that any increase in filling pressure should Desensitization Theory Summary produced an increase in the stroke volume and cardiac output.
Suarez et al. Similarly, Reeves et al. Reeves et al. Hence, for the classical model to be correct, cardiac output must always be maximal at maximal exercise regardless of PiO2, FiO2 or CaO2. Hence, any intervention such as anaemia or hypoxia that reduces CaO2, thereby threatening oxygen Desensitization Theory Summary to the exercising muscles, must be countered by acute changes, the principal aim of which must be to maintain oxygen delivery to the exercising muscles. Clearly, the exact opposite holds during chronic hypobaric hypoxia. It is also of interest that the skeletal muscle blood flow is unaltered at maximal exercise during acute anaemia, even though cardiac output is submaximal Koskolou et al. Rather, according to this model, the reduced PaO2 during hypoxia will reduce potential oxygen delivery to both the skeletal muscles and the heart.
Thus, several studies found that acute hypoxia decreases fhmax in both athletic and normally active men and women Drinkwater et al. Ekblom and colleagues Ekblom Desensitization Theory Summary al. The effect was due mainly to a decreased VS. More recently, Peltonen et al. Peltonen et al. Maximal heart rates follow Su,mary similar pattern and are submaximal at exhaustion Table2.
Furthermore, leg blood flow per heart beat, an indirect indicator of the stroke volume, rises progressively from hypoxia to normoxia to hyperoxia Table2. The finding that leg blood flow is Desensitizatlon increased during single-legged exercise during hypoxia, even though the cardiac output is submaximal, parallels the finding Desensitization Theory Summary acute anaemia Koskolou et al.
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Maximum heart rate is reduced, in a dose-dependant manner, in response to increasingly acute hypoxia, whereas maximal plasma norepinephrine and lactate concentrations are unchanged during acute hypoxia. Lundby et al.
A similar result has been reported during chronic hypoxia Kayser et al. However, this mechanism does not play a major role in the hypoxia-induced reduction of fhmax. The authors suggest that postganglionergic desensitization and not downregulation of cardiac adrenoreceptors is responsible for the early decrease in fhmax during hypoxia. As argued previously, the classical model proposed two separate mechanisms for fatigue during maximal exercise. First was the development of myocardial hypoxia causing a progressive cardiac failure. Clearly, this model cannot explain the fatigue of chronic hypobaric hypoxia, including the profound muscle weakness at altitude described by Pugh Pugh,or the inability of Peter Habeler and Reinhold Messner to walk upright to the summit of Mount Everest during their oxygen-less ascent, since i myocardial ischaemia does not occur during maximal exercise at extreme altitude Reeves et al.
If this extrapolation held good, a Desensitization Theory Summary climber Front Essays Eastern reached the summit of Mount Everest without supplementary oxygen would have no blood lactate. Clearly some other mechanism s Desensitization Theory Summary be operative, at least during chronic hypoxia. That myocardial ischaemia does not develop even during severe exercise in either hypoxia or normoxia Raskoff et al.
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To Desensotization myocardial oxygen consumption during hypoxia, a more complete extraction of O2 from the coronary blood flow compensates for the reduced CaO2 compared with Desensitization Theory Summary values. This again supports the theory that a constrainer exists specifically to terminate the exercise before myocardial ischaemia can develop. A possible reason why stroke volume falls during hypoxia, even when only a single leg is active Richardson et al.]
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