Final answer:
Positive-pressure ventilation involves air being forced into the lungs, creating higher pressure than that of the environment, which differs from negative-pressure ventilation where air is drawn into the lungs due to lower internal lung pressure.
Step-by-step explanation:
In contrast to negative-pressure ventilation, positive-pressure ventilation occurs when air is pushed into the lungs, creating a pressure that is greater than the atmospheric pressure. Negative-pressure ventilation involves expanding the thoracic cavity and creating negative pressure that allows air to diffuse into the lungs. Positive-pressure ventilation, by comparison, actively forces air into the lungs, increasing the intra-alveolar pressure to a level higher than the atmospheric pressure, which in turn inflates the lungs during ventilation.
Pulmonary ventilation is a process dependent on Boyle's Law, where pressure and volume have an inverse relationship. During inhalation, the diaphragm and intercostal muscles contract, increasing the thoracic volume and decreasing the pressure inside the lungs, hence creating a negative pressure relative to the outside, allowing air to flow into the lungs. Conversely, during exhalation, the lungs recoil and the thoracic volume decreases, causing an increase in pressure inside the lungs above atmospheric level (positive pressure) to push air out.