Hemodynamic effects of ventilation and ventilatory maneuvers

The cardiocirculatory-respiratory system is a complex and highly integrated system that balances the ever changing and often conflicting metabolic demands of the body in a smooth fashion over a remarkably wide range of metabolic demands and constraints that life creates. The system includes such varied functional structures as the left and right atria (LA and RA, respectively) and ventricles (LV and RV, respectively) and the pulmonary and systemic vasculature. It works in an environment of differential extravascular pressures that reflect the tissue surface pressures of the major body compartments, thorax, abdomen, cranium, and muscular tissue spaces. The system’s response to the varying demands and field conditions are profoundly influenced by myocardial reserve, vascular resistance, circulating blood volume, blood flow distribution, autonomic tone, and endocrinological processes, as well as by baseline lung volume and its change, intrathoracic pressure (ITP), and the surrounding pressures for the remainder of the circulation, as induced by the mechanical and spontaneous breath. It should not be surprising, therefore, that dramatically different hemodynamic responses to similar ventilatory maneuvers can occur among subjects. These concepts have been previously described by our group (1-13) and others (14-18). The reader is referred to these prior reviews for greater in-depth discussions of the specific physiologic details discussed below. This chapter will focus primarily on the clinical application of these principals in common condi- 184 Pinsky tions and as a physiological paradigm for the reader to understand better the subsequent chapters in Section IV for specific disease states