Initial orthostatic hypotension induced by squatting

C.T.P Krediet, W. Wieling

Department of Medicine, Academic Medical Centre, University of Amsterdam, Amsterdam (The Netherlands)

Case Reports

A 37-year old female patient, an enthusiastic horse rider underwent cardiovascular reflex assessment after losing consciousness. The episode occurred after she squatted to bandage the legs of her horse (a routine equine procedure to support the distal tendons in the extremities) and then stood up. The patient reported that before the loss of consciousness she saw black spots and felt lightheaded. She was unconscious for less than one minute and was well oriented when she regained consciousness [1].

During her medical examination, the patient was asked to mimic the procedure of bandaging the four legs of her horse. The Figure shows continuous non-invasively measured finger blood pressure changes at heart level using Finapres model 5 (TNO Biomedical Instrumentation, Amsterdam, The Netherlands) and instantaneous heart rate changes. The patient was asked to squat (Figure, white bar) for about 30 seconds and to stand up quickly (grey bar). This was repeated 3 times. After the fourth squat-stand manoeuvre the patient remained standing. Each time she stood up, she complained of the same symptoms she had originally experienced (black spots and light-headedness).

Based on this reproducible blood pressure change induced by the squat-stand manoeuvre and the patient’s recognition of symptoms similar to those she had experienced spontaneously, initial orthostatic hypotension was identified as the cause for her loss of consciousness [1]. Leg crossing with muscle tensing immediately after standing diminished the fall in blood pressure (Fig. 2).

The patient was advised to apply this manoeuvre in daily life. In follow up, she reported that she benefitted from this manoeuvre. Tensing of leg, abdominal and buttocks alone was found to be just as effective and more convenient. She had not lost consciousness since the cardiovascular reflex test.

blood pressure squatting
Fig 1. Continuous monitoring of blood pressure and instantaneous heart rate during 4 squad-stand manoeuvres
blood pressure squatting rising
Figure 2. Blood pressure changes induced by the squat-stand manoeuvre. Legcrossing and tensing of lower body muscles (lower panel) decreases the initial fall in blood pressure and abolishes symptoms of lightheadedness.

Editor's Comments

Rising erect from squatting is a considerable hemodynamic, i.e. orthostatic stress [2]. On average blood pressure in healthy young adults falls by 60 mmHg systolic and 40 mmHg diastolic with a nadir about 7 s after rising (Fig. 3) [3][4]. Mild symptoms of transient lightheadedness are often present.

Two factors are likely to be involved in the rapid fall in pressure. First, a sudden decrease in total peripheral resistance in the legs due to the ischemic effect of squatting enables a very rapid inflow of arterial blood in the legs. Secondly, marked pooling of blood in the venous vessels in the legs and abdomen, which have been squeezed in the squatting position results in a decrease in venous return and thereby in cardiac output. The combination of the two factors results in a rapid translocation of a large amount of arterial blood from the chest to the distensible venous capacitance system below the diaphragm. The accelerative force during rapid standing up may play an additional role in the fall in pressure [5].

Rising to erect from squatting is a recognised trigger for a faint in daily life (see Case 2 in this section). Squatting in combination with hyperventilation and straining can induce a faint in almost everybody (fainting lark) (see Case in this section 4). In the 1960-70’s rising to erect from the squatting position was widely reported in the German literature to assess initial orthostatic adjustments [6][7]. The squat-stand test was introduced recently in the English literature as an orthostatic stress test [8][9].

Treatment for symptomatic initial orthostatic hypotension is largely unknown. An increase in salt intake has been advised (see case 1 in this section). The present case and additional recent observations [10] strongly suggest that lower body muscle tensing immediately after standing up is effective to prevent the abnormally large initial fall in pressure upon standing.

 

initial orthostatic hypotension
Figure 3. Average intra-arterial blood pressure and heart rate changes induced by squatting in four 21-40 years old healthy males.[3]

References

  1. Parts of this case were published earlier: Krediet CT. Initial orthostatic hypotension in a 37-year old horse rider. Clin Auton Res. 2002; 12: 404. We thank Springer Verlag (Darmstadt, Germany) for permitting this reproduction.
  2. SHARPEY-SCHAFER EP. Effects of squatting on the normal and failing circulation. Br Med J. 1956 May 12;1(4975):1072-4. PubMed ID:13316071
  3. Wieling & van Lieshout unpublished data.
  4. Rossberg F and Penaz J. Initial cardiovascular response on change of posture from squatting to standing. Eur J Appl Physiol Occup Physiol. 1988;57(1):93-7. PubMed ID:3342800
  5. BROWN GE Jr, WOOD EH, and LAMBERT EH. Effects of tetra-ethyl-ammonium chloride on the cardiovascular reactions in man to changes in posture and exposure to centrifugal force. J Appl Physiol. 1949 Sep;2(3):117-32. DOI:10.1152/jappl.1949.2.3.117 | PubMed ID:18138999
  6. de Marées H. [Orthostatic immediate regulation]. Cardiology. 1976;61 suppl 1:78-90. DOI:10.1159/000169795 | PubMed ID:975151
  7. Barbey K,Barbey K, Kutcha W. Uber die orthostatische sofortregulation. Med welt 1966.
  8. Convertino VA, Tripp LD, Ludwig DA, Duff J, and Chelette TL. Female exposure to high G: chronic adaptations of cardiovascular functions. Aviat Space Environ Med. 1998 Sep;69(9):875-82. PubMed ID:9737759
  9. Rickards CA and Newman DG. A comparative assessment of two techniques for investigating initial cardiovascular reflexes under acute orthostatic stress. Eur J Appl Physiol. 2003 Nov;90(5-6):449-57. DOI:10.1007/s00421-003-0852-0 | PubMed ID:12883894
  10. Krediet CT, Wieling W. Physical counter maneuvers are effective in diminishing initial orthostatic hypotension. Clin Auton Res 2004;14:311-312
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