Valsalva Manoeuvre

Explain the response of the circulation to situations such as changes in posture haemorrhage, hypovolaemia, anaemia, intermittent positive pressure ventilation, positive end-expiratory pressure, and the Valsalva manoeuvre.

A Valsalva is forced expiration against a closed glottis. This can be achieved by increasing P_AW to 40mmHg for 15 seconds. This increase in intrathoracic pressure alters many haemodynamic parameters.

Phases

A Valsalva manoeuvre consists of four phases:

Phase I

• P_AW is increased to 40cmH₂O, with a corresponding increase in P_Thoracic
• SBP and DBP increase due to:
  • Compression of the aorta
  • Increased LV preload due to ejection of blood in the pulmonary vasculature

Phase II

• VR falls due to increased P_Thoracic
• CO falls due to decreased VR

• SBP and DBP fall due to decreased CO

• Baroreceptor activity is ↓ by the fall in BP, and SNS outflow increases, causing:

  • Increased HR
  • Increased SVR
    • BP therefore starts to recover late in Phase II

Phase III

• The Valsalva ceases, and P_AW returns to 0cmH₂O
• PVR rapidly drops as alveolar vessels re-expand
• SBP and DBP rapidly fall due to:
  • Decreased PVR causing decreased LV preload
  • Loss of high intrathoracic pressure compressing the aorta

Phase IV

• VR normalises
• CO normalises due to normal VR and PVR

• SBP and DBP transiently increase due to a normal CO entering a baroreceptor-driven high-SVR vascular bed

• Baroreceptors respond to high SBP an DBP by increasing vagal tone:

  • HR falls (reflex bradycardia)
  • BP falls

Abnormal Responses

Abnormal responses occur in cardiac failure and autonomic neuropathy.

CCF

In CCF a square-wave patten is produced:

• Increasing P_AW resulting in a sustained increase in SBP and DBP
• There is a slight decrease in SBP and DBP for the few seconds in phase III when airway pressure is released

Appears to be due to the increased circulating volume, as this difference resolves in venesected cardiac patients, and is demonstrated in normal individuals who are transfused to a high circulating volume.

Autonomic Neuropathy

Baroreceptor response to the Valsalva is minimal in both phase II and IV:

• In phase II, there is no compensatory increase in sympathetic outflow, so BP continues to fall until P_AW returns to 0mmHg
• In phase IV, there is no compensatory increase in vagal tone and so BP returns to normal without overshooting

References

1. Kam P, Power I. Principles of Physiology for the Anaesthetist. 3rd Ed. Hodder Education. 2012.
2. Judson WE, Hatcher JD, Wilkins RW. Blood Pressure Responses to the Valsalva Maneuver in Cardiac Patients with and without Congestive Failure. Circulation. 1955;11:889-899.