Orthostatic Intolerance

What is Orthostatic Intolerance (OI)?

Written by: Brenda Agwalama (Accredited Exercise Physiologist)

Orthostatic Intolerance is defined by the inability to maintain an upright posture, due to deficiencies in blood volume, skeletal muscle pump activation, and autonomic reflexes. Symptoms in those who suffer from OI are often relieved by reclining. OI can occur across all ages, but is more commonly diagnosed in women.


Types of Orthostatic Intolerance

OI is categorised as either acute or chronic.

Acute Orthostatic Intolerance: patients with acute OI experience temporary loss of consciousness, and posture, followed by rapid recovery. These episodes are often triggered by standing, heat, or emotion.

Chronic Orthostatic Intolerance: patients with acute OI experience symptoms on most or all days.

Causes of Orthostatic Intolerance:

  • Changes in heart rate, blood pressure, and cerebral blood flow due to abnormalities in blood volume control, the cardiovascular system, the nervous system, and circulation control system
  • Prolonged periods of stable upright posture
  • Being in a warm environment
  • Low blood volume
  • Poor skeletal and respiratory muscle pumps
  • Dysregulation of the autonomic nervous systems
  • Other factors such as gravitational and exercise deconditioning, immune-mediated disease, mast cell activation, and central hypovolemia

Signs and Symptoms include but are not limited to:

  • Loss of consciousness
  • Lightheadedness
  • Pallor
  • Visual disturbances
  • Fatigue
  • Tachycardia
  • Bradycardia
  • Hypotension
  • Headaches
  • Weakness
  • Nausea
  • Heat intolerance
  • Diaphoresis

Orthostatic Intolerance and Exercise

A tailored exercise program should involve goals that are specific to improving aerobic fitness, peripheral muscles mass, and cardiovascular function, along with decreasing the negative effects of OI.

Aerobic Training in Orthostatic Intolerance

Those affected by OI are more likely to avoid physical activity, as a result of their symptoms being exacerbated upon standing. However, it has been found that OI symptoms and quality of life improve following exercise training. This is attributed to the aerobic adaptations associated with improved aerobic capacity, an increase in plasma volume, increased cardiac size and mass, and stroke volume.

Resistance Training in Orthostatic Intolerance

Resistance training assists with improving muscular strength and endurance, bone density, and body composition. Several studies have shown that resistance training can lead to increased blood volume and lower body negative pressure tolerance (LBNP), decreased sensitivity of the carotid baroreceptor cardiac reflex response, and decreased venous pooling.

Exercise Prescription in Orthostatic Intolerance

A Physical Activity Readiness Questionnaire (PAR-Q) should be conducted by the practitioner prior to any exercise participation. The practitioner should include assessment of the patients baseline orthostatic tolerance and fitness levels. As with any exercise prescription, initial assessment is essential in devising and implementing an appropriate exercise program and the program should be regularly reassessed.

Short and long-term exercise training have demonstrated positive effects on OI. Evidence suggests that light to moderate aerobic exercise coupled with gradual integration of progressive resistance training is most effective. Exercise prescription should be evidenced based including progression of frequency, intensity, and duration in order to assist individuals with OI achieve their orthostatic and fitness goals.