The Rebbe’s handwritten response to a husband who asked for a bracha regarding his wife’s health:
במקרים רבים דומים לזוג’ תי’ – הוספה בשימת לב הבעל לאשתו מוסיפה בבריאותה וכו’.
כמובן – הוספה שתרגיש בה.
In many cases similar to that of your wife ‘שתחי, an increase in the husband’s attention to his wife adds in her health, etc.
Obviously, the addition has to be one she can feel.” ■