Normal Sinus Rhythm (NSR)

Definition - What does Normal Sinus Rhythm (NSR) mean?

Normal sinus rhythm (NSR) is a physiological function of the heart rate that begins at the sinus node, the locus of bioelectric activity that stimulates the chambers called the atria (top) and its corresponding ventricles (bottom) to pump blood through the body. In medicine, normal sinus rhythm serves as a criterion in assessing the relative health of the heart muscle where baseline metrics range between 60 and 99 beats per minute.

WorkplaceTesting explains Normal Sinus Rhythm (NSR)

Normal sinus rhythm can fluctuate to the extent that the electrical impulses are proportionate to atrial and ventricular contractions that quicken or slow heart rate. An irregular heartbeat can reflect variables including sustained exertion (i.e., exercise), homeostatic response (i.e., fever), pathological condition (i.e., anemia) and environmental circumstances related to stress. Sinus rhythm abnormalities fall into two categories including bradycardia (slow heart rate) and tachycardia (fast heart rate).

Sinus rhythm deviations can also indicate an otherwise normal heart rate, for example, physical exercise induces sinus tachycardia to ensue. As a result, maximal cardiac output helps expedite the distribution of oxygenated blood to specific muscles in the body, offsetting fatigue. Conversely, bradycardia is a biological consequence of normal sleep patterns as heart rate decreases, suspending motor activity.

Sleep disorders can influence heart rate by disrupting breathing patterns causing an elevation in blood pressure and depletion of oxygen levels in the blood. For instance, obstructive sleep apnea (OSA) is a common sleep disorder characterized by intermittent breathing cessations, accelerating heart rate to compensate the deficit of oxygen needed to maintain normal sinus rhythm. In the workplace, sleep apnea is a prevalent health concern that can lead to excessive daytime sleepiness, chronic fatigue, depression, and impaired cognition. A continuous positive airway pressure (CPAP) device is the preferable therapeutic modality in treating OSA-related cases, in turn, regulating heart rate.

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