"systolic up-rush (or the diastolic slump)"

This line links to the preceding sentence; “This adventure was just one of those scratchy heartbeats on the line of my life.” Systolic and diastolic refers to the pressure of the suction in, and the pumping out, of the flow of blood in the heart. The image links the jagged shape of a heart monitor to the peaks and troughs of a mountain range and hence suggests by contrast that life on the plane, devoid of risk, is approximate to flat-lining.