Heart Rate During the Valsalva Maneuver

The 4 Phases

Key Mechanisms

"The fall in blood pressure is sensed and sympathetic stimulation and parasympathetic withdrawal brings the blood pressure back up toward baseline and the heart rate elevates."

• Braunwald's Heart Disease, p. 1264

"The blood pressure therefore rises above normal, and this stimulates the baroreceptors, causing bradycardia and a drop in pressure to normal levels."

• Ganong's Review of Medical Physiology, p. 592

"With the release of intrathoracic pressure, the venous return, stroke volume, and blood pressure rise to higher-than-normal levels; reflex parasympathetic influence then predominates and a bradycardia results."

• Adams and Victor's Principles of Neurology, p. 554

Normal Blood Pressure Response (with pulse rate as reciprocal)

Valsalva Ratio (Clinical Use)

• Normal ratio: ≥ 1.5 (varies slightly by age)
• Used to test autonomic integrity - specifically parasympathetic (vagal) function
• Failure of HR to rise during straining (Phase II) → sympathetic dysfunction
• Failure of HR to slow during BP overshoot (Phase IV) → parasympathetic (vagal) dysfunction

Abnormal Response Pattern

• The fall in BP during straining is not corrected (no sympathetic compensation)
• There is no BP overshoot on release
• Therefore no Phase IV bradycardia occurs
• Heart rate changes are absent or blunted throughout

Summary

Interpreting Abnormal Valsalva Responses in Autonomic Testing

The Two Core Scores

• Normal: ≥ 1.5 in young adults; decreases with age (≥ 1.2 by age 40, approaches 1.04 beyond age 60)
• Measures the parasympathetic arm of the baroreflex
• Diminished in diabetes, α-synuclein disorders (Parkinson's, MSA, DLB), and with anticholinergic medications

• The magnitude of the BP drop during Phase II, BP recovery time, and BP overshoot in Phase IV
• Measures the sympathetic (adrenergic) arm of the baroreflex

Pattern Recognition: 4 Abnormal Response Types

Type 1 - Adrenergic (Sympathetic) Failure

"Large hypotension in early Phase II and lack of pressure recovery and pressure overshoot in late Phase II and Phase IV can be observed in patients with orthostatic hypotension (α-adrenergic failure). Dramatic drops in BP in Phase II in subjects with adrenergic dysfunction may even lead to syncope."

• Physiology and Clinical Examples of the Valsalva Manoeuvre (Sandroni et al. 1985 cited)

"Dysfunction of the SNS is implicated if exaggerated and prolonged hypotension develops during the forced expiration phase (≥50% fall from resting MAP). In addition, the overshoot at the end of the Valsalva maneuver is absent."

• Barash, Cullen, and Stoelting's Clinical Anesthesia, p. 1068

Type 2 - Vagal (Parasympathetic) Failure

"Failure of the heart rate to increase during the positive intrathoracic pressure phase of the Valsalva maneuver points to sympathetic dysfunction, and failure of the rate to slow during the period of blood pressure overshoot points to a parasympathetic disturbance."

• Adams and Victor's Principles of Neurology 12th Ed., p. 554

"Dysfunction of the PNS can be assumed if the HR does not respond appropriately to the blood pressure changes."

• Barash, Cullen, and Stoelting's Clinical Anesthesia, p. 1068

Type 3 - Complete Autonomic Failure (combined sympathetic + parasympathetic)

"In patients with autonomic failure, the fall in blood pressure is not aborted during the last few seconds of increased intrathoracic pressure, and there is no overshoot of blood pressure when the breath is released."

• Adams and Victor's Principles of Neurology 12th Ed., p. 554

"In patients whose sympathetic nervous system is not functional, heart rate changes still occur because the baroreceptors and the vagi are intact. However, in patients with autonomic insufficiency, a syndrome in which autonomic function is widely disrupted, the heart rate changes are absent."

• Ganong's Review of Medical Physiology, p. 592

Type 4 - "Square Wave" Response (Elevated Venous Pressure / Cardiac Failure)

Summary Interpretation Table

Confounders to Account For

• Age: VR normally decreases with age - always compare to age-matched norms. Values approaching 1.04 can be normal over age 60.
• Medications: Anticholinergics blunt VR; antihypertensives, alpha- and beta-blockers directly affect both arms of the baroreflex.
• Technique: Suboptimal straining pressure (<40 mmHg) or duration (<15 s) may prevent late Phase II from forming, yielding a false-positive abnormal result.
• Position: Supine position increases the incidence of abnormal BP responses; standardize position between tests.

Clinical Conditions Causing Abnormal Responses

Clinical Significance of the Valsalva Maneuver

1. Autonomic Function Testing

"The integrity of the baroreceptor reflex can be tested with the Valsalva maneuver, which is expiring against a closed glottis as during coughing, defecation, or heavy lifting."

• Costanzo Physiology 7th Edition, p. 172
• Valsalva Ratio (max HR during maneuver ÷ lowest HR in 30 s after) = parasympathetic (vagal) function
• Adrenergic Index (magnitude of BP fall + overshoot) = sympathetic (adrenergic) function

2. Termination of SVT (Supraventricular Tachycardia)

"During wide-QRS tachycardias with a 1:1 relationship between the P waves and QRS complexes, vagal influence can terminate or slow a supraventricular tachycardia (SVT) that depends on the AV node for perpetuation."

• Braunwald's Heart Disease, p. Physical Examination section

"Mean changes in bradycardia are greatest with the Valsalva maneuver... As the maneuver is sustained, vagal tone is increased, thereby leading to a compensatory decrease in SA and AV conduction."

• Roberts and Hedges' Clinical Procedures in Emergency Medicine

3. Dynamic Cardiac Auscultation - Murmur Differentiation

"The majority of murmurs decrease in intensity during the strain phase of the maneuver. Two notable exceptions are the murmurs associated with MVP and HOCM, both of which become louder during the Valsalva maneuver."

• Harrison's Principles of Internal Medicine 22E, p. 332

"The left ventricular outflow tract obstruction of HOCM is dynamic... Preload is decreased during the straining phase of the Valsalva maneuver, which leads to an increase in the degree of outflow obstruction with an associated increase in the intensity of the murmur."

• Frameworks for Internal Medicine

4. Physiological Occurrences (Normal Life)

• Defecation / straining - most common physiological Valsalva
• Heavy lifting / weight training
• Coughing and sneezing
• Childbirth (second stage of labor)
• Playing wind instruments
• Ear pressure equalization (e.g., during air travel or diving)

5. Diagnosis of Heart Failure ("Square Wave" Response)

6. Urological Applications

• Areflexic/neurogenic bladder with low outlet resistance
• T11-L2 spinal cord injury with sympathetic denervation
• Detrusor underactivity (DUA) with incompetent sphincter

"'Voiding' by the Credé or Valsalva maneuver is generally discouraged because it is non-physiologic... The best chance for success is in the patient with an areflexic bladder and some degree of outlet denervation."

• Campbell Walsh Wein Urology

7. Stress Incontinence Provocation

8. Ophthalmology - Valsalva Retinopathy

9. Anesthesia Significance

• Managing elevated ICP (straining increases intracranial pressure - should be avoided)
• Predicting hemodynamic instability under general anesthesia
• Assessing baroreflex sensitivity preoperatively

Summary Table

Baroreceptor Reflexes

Overview

"The baroreceptor mechanisms are fast, neurally mediated reflexes that attempt to keep arterial pressure constant via changes in the output of the sympathetic and parasympathetic nervous systems to the heart and blood vessels."

• Costanzo Physiology 7th Ed., p. 169

1. Anatomy of Baroreceptors

1. Carotid sinus - a small dilation of the internal carotid artery just above the carotid bifurcation
2. Aortic arch - in the adventitia of the aortic wall

• Carotid sinus baroreceptors → Hering's nerve → Glossopharyngeal nerve (CN IX) → Nucleus tractus solitarius (NTS) of medulla
• Aortic arch baroreceptors → Aortic depressor nerve → Vagus nerve (CN X) → NTS of medulla

"Baroreceptors are spray-type nerve endings that lie in the walls of the arteries and are stimulated when stretched... extremely abundant in the carotid sinus and the aortic arch."

• Guyton and Hall Textbook of Medical Physiology

• Carotid sinus baroreceptors: respond to both increases AND decreases in arterial pressure; more sensitive; threshold ~50 mmHg; saturates at ~200 mmHg
• Aortic arch baroreceptors: primarily responsive to increases in arterial pressure; operate at pressure levels ~30 mmHg higher than carotid receptors; continue responding at pressures where carotid receptors have saturated

2. Firing Characteristics

• Threshold: ~50 mmHg (no activity below this)
• Maximum firing: ~200 mmHg (throughout the cardiac cycle)
• Most sensitive to: rapid changes in pressure (rate of change), not just absolute pressure
• Pulsatile pressure sensitivity: a fall in pulse pressure without change in mean pressure still reduces firing and triggers a pressor response
• Firing increases during systole and decreases during diastole (phasic pattern)

"The strongest stimulus for the baroreceptors is a rapid change in arterial pressure!"

• Costanzo Physiology, p. 170

"The baroreceptors respond rapidly... the rate of impulse firing increases in the fraction of a second during each systole and decreases again during diastole. Furthermore, the baroreceptors respond much more to a rapidly changing pressure than to a stationary pressure."

• Guyton and Hall Textbook of Medical Physiology

3. Central Processing - The Medullary Circuit

"NTS neurons excite neurons in the CVLM. These CVLM neurons release GABA into the RVLM to reduce the firing rate of these [sympathetic] neurons. Excitatory projections also extend from the NTS to the vagal motor neurons. Thus, increased baroreceptor discharge inhibits the tonic discharge of sympathetic nerves and excites the vagal innervation of the heart. These neural changes produce vasodilation, venodilation, hypotension, bradycardia, and a decrease in cardiac output."

• Ganong's Review of Medical Physiology, p. 589

• Vasoconstrictor center (C1/RVLM): upper medulla + lower pons → sympathetic → arteriolar and venous constriction
• Cardiac accelerator center: sympathetic → increases SA node firing, AV conduction velocity, and contractility
• Cardiac decelerator center: parasympathetic (vagus) → decreases SA node firing rate

4. Integrated Reflex Arc

Response to INCREASED arterial pressure (e.g., acute hypertension):

1. ↑ BP → ↑ stretch → ↑ baroreceptor firing rate (CN IX, CN X → NTS)
2. NTS activates CVLM → CVLM GABAergically inhibits RVLM → ↓ sympathetic outflow
3. NTS also excites vagal motor nuclei → ↑ parasympathetic outflow
4. Net effects:
   • ↓ Heart rate (vagus on SA node)
   • ↓ Contractility (↓ sympathetic to myocardium)
   • Arteriolar vasodilation → ↓ TPR
   • Venodilation → ↑ unstressed volume → ↓ venous return
   • ↓ Cardiac output + ↓ TPR → BP falls back toward normal

Response to DECREASED arterial pressure (e.g., hemorrhage, standing up):

1. ↓ BP → ↓ stretch → ↓ baroreceptor firing
2. Less CVLM activity → less GABA inhibition of RVLM → ↑ sympathetic outflow
3. Less NTS output to vagal nuclei → ↓ parasympathetic outflow
4. Net effects:
   • ↑ Heart rate (β1 on SA node)
   • ↑ Contractility (β1 on myocardium)
   • ↑ TPR (arteriolar vasoconstriction via α1)
   • Venoconstriction → ↓ unstressed volume → ↑ venous return
   • ↑ Cardiac output + ↑ TPR → BP rises toward normal

5. Responses in Specific Situations

Response to Hemorrhage

Response to Standing (Orthostatic stress)

"Immediately on standing, arterial pressure in the head and upper body tends to fall, and marked reduction could cause loss of consciousness. However, the falling pressure at the baroreceptors elicits an immediate reflex, resulting in strong sympathetic discharge throughout the body."

• Guyton and Hall

6. "Pressure Buffer" Function

"A primary purpose of the arterial baroreceptor system is to reduce the minute-by-minute variation in arterial pressure to about one-third of what would occur if the baroreceptor system were not present."

• Guyton and Hall

7. Baroreceptor Resetting

• Chronic hypertension is maintained rather than corrected by the baroreceptor reflex
• The mechanism involves decreased mechanoreceptor sensitivity, not resetting of central CNS vasomotor centers

"In chronic hypertension, the baroreceptors do not 'see' the elevated blood pressure as abnormal. In such cases, the hypertension will be maintained, rather than corrected, by the baroreceptor reflex."

• Costanzo Physiology, p. 170

8. Low-Pressure (Cardiopulmonary) Baroreceptors

• Right atrium and great veins (Bainbridge reflex)
• Pulmonary arteries
• Atria (volume/stretch sensors)

• ↑ Atrial stretch → ↑ HR (Bainbridge reflex)
• ↓ Venous pressure → ↓ HR

"Venous baroreceptors sample preload by stretch of the atrium. Arterial baroreceptors survey resistance, or afterload, as reflected in the mean arterial pressure. Afterload and preload produce opposite effects on CO; thus the venous and arterial baroreceptors produce opposing effects after a similar stretch stimulus."

• Barash, Cullen and Stoelting's Clinical Anesthesia

9. Clinical Relevance Summary