( ( The ( decreased distensibility ) ) ( ( means ( that ( ( ( ( ( ( the increase ) ( in ( volume ( for ( ( unit change ) ( in pressure ) ) ) ) ) ) ( is ( ( less than ) normal ) ) ) and ) ( , ( therefore , ) ) ) ( ( the ( same ( stroke volume ) ) ) ( would ( ( raise ( ( ( the pressure ) more ) ( during systole ) ) ) ( when ( ( the arteries ) ( are ( ( hardened than ) ( in ( normal arteries ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (VBN decreased) (NN distensibility)) (VP (VBZ means) (SBAR (IN that) (S (S (NP (NP (DT the) (NN increase)) (PP (IN in) (NP (NP (NN volume)) (PP (IN for) (NP (NP (NN unit) (NN change)) (PP (IN in) (NP (NN pressure)))))))) (VP (VBZ is) (ADJP (ADVP (RBR less) (IN than)) (JJ normal)))) (CC and) (PRN (, ,) (ADVP (RB therefore)) (, ,)) (S (NP (DT the) (JJ same) (NN stroke) (NN volume)) (VP (MD would) (VP (VB raise) (PP (ADVP (NP (DT the) (NN pressure)) (RBR more)) (IN during) (NP (NN systole))) (SBAR (WHADVP (WRB when)) (S (NP (DT the) (NNS arteries)) (VP (VBP are) (VP (VBG hardened) (IN than) (PP (IN in) (NP (JJ normal) (NNS arteries))))))))))))) (. .)))
The decreased distensibility means that the increase in volume for unit change in pressure is less  than normal and, therefore, the same stroke volume would raise the pressure more during systole when the arteries are hardened than in normal arteries.
(ROOT (S (S (VP (VP (VBG Decreasing) (NP (NP (DT the) (NN volume)) (PP (IN of) (NP (DT a) (NN gas))))) (CC and) (VP (VBG keeping) (NP (NP (NN everything)) (NP (RB else) (DT the) (JJ same)))))) (VP (MD will) (VP (VB cause) (NP (PRP$ its) (NN pressure) (S (VP (TO to) (VP (VB increase))))))) (. .)))