(Chest 1994; 106:236-43) AHPR = acute hypoxic pressor response; cGMP = guanosine cyclic monophosphate; NO = nitric oxide; PAP = pulmonary arterial pressure; PVR = pulmonary vascular resistance; PVSMC = pulmonary vascular flat muscle cell Pulmonary hypertension is a haunt hemodynamic complication associated with a wide variety of respiratory a whole s disorders whose only common physiologic abnormalities are alveolar hypoxia and inferable [i]or[/i] inferrible arterial hypoxemia of long-term duration.

(Chest 1994; 106:236-43)

AHPR = acute hypoxic pressor response;

cGMP = guanosine cyclic monophosphate;

NO = nitric oxide;

PAP = pulmonary arterial pressure;

PVR = pulmonary vascular resistance;

PVSMC = pulmonary vascular flat muscle cell

Pulmonary hypertension is a haunt hemodynamic complication associated with a wide variety of respiratory a whole s disorders whose only common physiologic abnormalities are alveolar hypoxia and inferable [i]or[/i] inferrible arterial hypoxemia of long-term duration. as it is disease processes include the alveolar hypoventilation syndrome neuromuscular disorders, kyphoscoliosis, and sharp obstructive lung diseases.(1) Similar findings have been observ in humans residing at high altitude.(2) In contrast to the pulmonary circulatory reply to acute hypoxia, prolonged durations of hypoxic exposing experimentally or associated with human disease states cause a persistent elevation in pulmonary arterial urgency (PAP) which is not immediately or totally correctable concerning improvement in oxygen concentrations to normal values. A variety of influences can contribute to the increase in PAP, including acute respiratory acidosis and the customary systemic response of secondary polycythemia. However, the focus of this review will center upon the local effects of chronic alveolar hypoxia onward the pulmonary vasculature directly, which are in major part the main determinants of the increase in pulmonary vascular resistance (PVR) The sustained elevation in PAP is notion to be mediated through couple pathophysiologic vascular mechanisms: (1) persistent vasoconstriction and (2) vascular structural remodeling.(3) The combination of these processe causes vascular luminal narrowing and tube obliteration that reduce pulmonary vascular surface area to the critical stage necessary for the development of pulmonary hypertension. Although the exact contribution of either mechanism to the elevation in PVR will vary from case to case and from disease to disease, their combined power on PAP is an established cause of morbidity resulting from cor pulmonale. Given the importance of each individual proces a detailed review of relevant or probable etiologic mechanisms appeared warranted with special emphasis directed toward circulating and future therapies.

COMPARISONS: CLINICAL AND EXPERIMENTAL

Accurately defining the complexity of the pulmonary vascular rejoinder to prolonged durations of reduc oxygen tension has been complicated from the myriad of factors demonstrated to have significance in disease unfolding both clinically and experimentally. Interspecies and intraspecies variation has been observ in virtually each aspect of study ranging from experimental protocol to rises Bovine and porcine species are quite susceptible to the pulmonary hemodynamic complications of hypoxia in contrast to the hyporesponsiveness of dogs and sheep. Within the same species, neonatal calves exhibit brisk hemodynamic rejoinders and dramatic structural changes when raised at altitude compared with similarly expos adult animals.(4) Similar age and sex differences in this same answer have been noted in rats.(5) In small animal species, reductions in inspired oxygen concentrations to approximately half-normal (normobaric or hypobaric) consistently elicit structural and hemodynamic alterations evident as early as 3 days following exposing with full development at 2 weeks.(6) Interestingly, intermittent hypoxic exposing in rats for as little as 4h/d is equally effective in producing vascular abnormalities as those evident about continuous exposure.(7) Less severe qualitys of hypobaric hypoxia will show sustained pulmonary hypertension in cattle. However, susceptibility to the meanings of prolonged hypoxia in this species is not universal moreover appears to be determined somewhat by way of genetic influences since selective breeding can segregate animals into either hypoxia-resistant or hypoxia-sensitive groups(8)

Obligatory disparities exist between experimental animal studies and the progress to maturity of pulmonary circulatory changes observ in human disease states. Excluding residence at high altitude, the progress to maturity of chronic hypoxic pulmonary hypertension in humans does not portray by action a distinct disease entity, moreover rather occurs as a complication of another primary disease proces with its acknowledge unique set of associated variables. For example, the interaction of inflammatory cytokines associated with chronic bronchitis may be an additional stimulus modulating vascular abnormalities.(9) For the most numerous part, the progressive deterioration in alveolar oxygen concentrations is notion to represent a chronic, slowly evolving proces associated with local inhomogeneity in the grade of hypoxia. This contrasts with the abrupt attack and short duration of generalized hypoxia make use ofed experimentally. In addition, defined openings in the levels of alveolar hypoxia necessary for the induction of either vascular proces have not been established in humans. Finally, the late storm of clinical manifestations resulting from this hemodynamic abnormality and the lack of identifiable indices predictive of disease progressive growth suggest that studies and therapies directed at established disease may not veraciously reflect earlier etiologic mechanisms.

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