The left ventricle’s (LV) pressure-volume (P-V) loop visually represents an important relationship between the chamber’s pressure and volume over a single cardiac cycle. In the following diagram, systole is red, and diastole is blue. The P-V loop consists of four events:
The right ventricle (RV) is designed to be a compliant volume chamber that pumps against a low-pressure, low-resistance pulmonary arterial (PA) system. RV-PA coupling refers to the proportional alignment between RV contractility and afterload. In situations of increased RV afterload like pulmonary hypertension, the RV can adapt (e.g., anatomic remodeling…
The absolute and relative refractory periods refer to the intervals during which the cardiac cells are either entirely or partially unresponsive to further stimulation, respectively. The refractory periods are crucial in regulating the timing and rhythm of the heart’s contractions. Suppose a stimulus causes the transmembrane potential (TMP) to reach…
A patient’s breathing pattern can help guide response to therapies and diagnostics. Normal breathing is regular and comfortable at a rate of 12-20 breaths per minute (bpm).
The left ventricle’s (LV) variously arranged muscle fibers twist and contract during systole, storing potential energy as blood is ejected (imagine wringing water out of a towel). This stored energy is released in diastole: an energy-dependent myocardial relaxation divided into four phases.
Sodium (Na) fluctuations portend increased in-hospital death for ICU patients, and when working them up, it’s essential to determine if these disorders are acute or chronic (> 48 hours or unknown duration). For hypernatremia ([Na] > 145 mEq/L), think about situations where there is a free water deficit (FWD) –…
To maximize gas exchange, well-ventilated alveoli (V) should be associated with good pulmonary capillary blood perfusion (Q). This is the idea behind V/Q matching. Gravitational forces create heterogeneity perfusing dependent portions of the lung better – the lung base in the upright position, and the posterior lung in the supine…
In order for the heart muscle to actually contract, the physiological process of excitation-contraction coupling must occur via an action potential propagated through the myocardium. Normally, these muscle cells have a resting transmembrane potential (TMP) around -90 mV (more negative intracellularly than extracellularly). This gradient is created and changed by…
With all the discussion surrounding antibody production after receiving a COVID-19 vaccine, let’s talk about the structure of an antibody.
The P/F ratio is a simple way to assess the severity of hypoxemia. It’s the ratio of the PaO2 (arterial oxygen partial pressure obtained from an arterial blood gas) to the FiO2 (fraction of inspired oxygen expressed as a decimal). For example, a person breathing room air (21% oxygen, or…