Tonus coronary

The compressive effect is due to the transmural pressure drop P, (y)-PJj, t) across the microvessels. A negative transmural pressure drop will generate collapse of the vessel and halt the flow in the vessel. The rigidity of the vessel s wall determines its resistance to collapse and determines the transmural pressure which is associated with the collapse phenomena. The combination of all these parameters determines the well known spatial dependence of P f on the LV pressure and the coronary tonus (Bellamy, 1978 1980 Sherman, 1980). 

An aromatized alkaloid of this derivation, papaverine (31) is the most important alkaloid of the BIQ group from the pharmacological point of view. Papaverine inhibits aldol reductase, GABA and glucose response in chemosensory cells, and phosphodiesterase (Wink, 1993). In vivo, this alkaloid decreases the tonus of the smooth muscle, increases coronary artery flow, and causes dilation. Papaverine has a beneficial effect on angina pectoris. This aromatic isoquinoline alkaloid is neither narcotic nor addictive (Cordell, 1981). Papaverine has an LD50 i.v. in mouse of 27.5 mg/kg. Demethylpa-paverine inhibits aldose reductase (Wink, 1993). 

The above models yield quantitative descriptions of the local stress, strain and strain rate within the muscle as well as the instantaneous sarcomere length distribution. The local intramural pressure (y, t), together with the tonus of the small vessels T ( (y), determine the resistance of the coronary bed and thus determine the nature and magnitude of the coronary flow in the wall. The local energy demand is calculated from the local stress, strain rate and sarcomere length and, assuming aerobic metabolism, is expressed here in terms of the oxygen demand. 

The calculation procedure is based on seeking, for each layer, a value of (y) which corresponds to PVOj (y) = 20 mmHg. This represents a control mechanism which affects the coronary resistance by changing the microvascular tonus according to the local PO2 value. No hypoxia is assumed to occur (i.e. (y) = MVOj... 

After the distribution of the transmural vascular tonus, (y), was determined, the spatial distribution of the time dependent and time-averaged coronary blood flow were calculated and plotted. The calculated relations between the average coronary flow, the coronary venous oxygen tension and the oxygen content are summarized below. 

Burns JW, Coveil JW (1972) Myocardial oxygen consumption during isotonic and isovolumic contractions in the intact heart. Am J Physiol 223 6 1491-1497 Cross CE, Rieben PA, Salisbury PF (1970) Coronary driving pressure and vasomotor tonus or determinants of coronary blood flow. Circ Res 9 589-600... 

The coronary resistance at each point y is assumed to vary between (y) (maximum vasodilatation) and (y) (maximum vasoconstriction). A regulatory function. T f (y), ranging between 0 and 1 represents the tonus of the wall and related to the coronary resistance by ... 

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