It is well known among professional trumpeters that playing high loud notes for more than a few seconds may cause dizziness or occasionally 'black-out.' Indeed, many leading orchestras carry an assistant or 'mate' to take over from the first trumpet in prolonged difficult passages...

Apart from the discomfort of occasional dizzy sensations or black-outs, trumpet players are not likely to come to any harm. Vasodilation from heat or previous hyperventilation will exaggerate the effects of a given intrathoracic pressure. It is better to sit than stand, but the strict supine posture, which would be better still, seems hardly feasible. For orchestras in severe financial difficulties it might be possible to dispense with the assistant or 'mate' if the trumpeter wore a pilot's pressure-suit, which could be surreptitiously inflated by a switch on the conductor's desk.