Final answer:
The Valsalva manoeuvre is a voluntary action used to increase intra-abdominal pressure, aiding in defecation. It should be avoided in people with certain health conditions like cardiovascular issues and glaucoma, due to the potential for it to cause abrupt changes in blood pressure and exacerbate these conditions.
Step-by-step explanation:
The Valsalva manoeuvre is a technique involving a voluntary contraction of the diaphragm and abdominal wall muscles, with a closing of the glottis, which increases intra-abdominal pressure. This pressure can be used to facilitate certain processes, such as defecation, by aiding the contractions of the rectal muscles. However, although it can be beneficial in the right context, it might not always be recommended because it can lead to other health issues.
There are some situations where the Valsalva manoeuvre might be advised against. For example, individuals with cardiovascular conditions may be at risk because the manoeuvre can lead to abrupt changes in blood pressure and heart rate, potentially causing dizziness, fainting, or even a cardiac event in those who are susceptible. Additionally, the increased pressure in the chest cavity can reduce blood flow back to the heart. Another consideration is for those with eye conditions such as glaucoma, where increased pressure could exacerbate the condition.