Vomiting, or emesis, is a protective reflex that expels potentially harmful substances from the upper gastrointestinal tract. This complex action is centrally coordinated in the brainstem and involves muscular and nervous system responses. The effect of vomiting on the heart rate is dynamic, not uniform. Heart rate can temporarily decrease during the initial phase, but generally increases during the physical act and may remain elevated afterward due to systemic consequences.
The Immediate Vagal Response
The initial phase, often accompanying the sensation of nausea, is governed by the parasympathetic nervous system. This phase is characterized by stimulation of the vagus nerve, which extends from the brainstem to the abdominal organs. Activation of the vagus nerve typically triggers a slowing of the heart rate, a condition known as bradycardia.
This vagal response is also responsible for other involuntary symptoms experienced before the actual expulsion. Increased salivation, pallor, and sweating are common signs that the parasympathetic system is initiating the emetic reflex. This slowing of the heart is usually brief and is a neurocardiogenic reaction to the initial trigger.
Heart Rate Changes During the Physical Act
The moment of retching and expulsion shifts the body’s control toward the sympathetic nervous system, often called the “fight or flight” response. The physical act itself is a forceful, highly coordinated muscular effort involving the diaphragm and abdominal wall muscles. This intense physical strain immediately elevates the heart rate, resulting in temporary tachycardia.
Furthermore, the surge of adrenaline and other stress hormones caused by the sympathetic activation contributes to the rapid increase in heart rate and blood pressure. This temporary increase in heart rate is the body’s natural response to both the physical exertion and the stress of the event.
Delayed Effects: Dehydration and Electrolyte Loss
Prolonged or repeated vomiting can lead to a sustained rapid heart rate that lasts long after the act is over. This delayed effect is primarily due to the loss of body fluids and key electrolytes. Loss of fluid volume results in dehydration, which decreases the total volume of blood circulating through the body.
The heart must then work harder, beating faster (sustained tachycardia), to circulate the diminished blood volume and maintain blood pressure and oxygen delivery. Vomiting also depletes electrolytes such as potassium, sodium, and magnesium, which are crucial for the heart’s electrical stability. An imbalance in these minerals can directly interfere with the heart’s rhythm, potentially causing palpitations or irregular beats.
When Rapid Heart Rate Becomes a Medical Concern
While a temporary increase in heart rate during vomiting is expected, a persistently rapid heart rate requires attention. If the heart rate remains elevated above 100 to 120 beats per minute after vomiting has stopped and the person is resting, it may indicate severe dehydration or a significant electrolyte disturbance.
Other serious symptoms to monitor include chest pain, shortness of breath, or feeling dizzy when standing up. An inability to keep liquids down for more than a few hours, or signs of confusion and extreme thirst, suggests a severe fluid deficit. These symptoms warrant immediate medical evaluation, as they indicate dangerous stress on the circulatory system from fluid loss.