Respiratory Arrhythmia
also called Sinus Arrhythmia is a variation of the
Heart Rate with respiration. Heart rate
increases with inspiration and decreases with expiration it's a physiological phenomenon and perhaps useful for the body as you don't want to wast heart beats when you have less alveolar ventilation

Bain
Pulsus Paradoxus
is
decreased Systolic Pressure [hence pulse amplitude] during inspiration,
--if the decrease is less than 10 mmHg then it's physiological [it happens because at inspiration your lung vessels expand pooling more blood and so less venous return to the LEFT atrium so decreased systolic pressure another proposed mechanism of pulsus paradoxus is that during inspiration the right heart is filled with blood and if there no space for it to expand because of restrictive heart or an overinflated lungs then it will push on the left ventricle decreasing its end diastolic volume and thereby decreasing systolic blood pressure]
--if more than 10 then look for the following conditions:
Cardiac temponade or pericarditis, Asthma Croup and COPD, also Obstructive sleep apnea
You may want to know about
- Pulsus Alternans [beat to beat variation in pulse pressure seen in systolic dysfunction],
- Pulsus Parvus [weak upstroke seen in hypovolemia],
- Pulsus Bisferiens [double pulsation during systole seen in LV dysfunction],
- Pulsus Tardus [delayed upstroke, seen in AS]